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Chronic toxicity is a property exhibited by toxins which can be dangerous over a prolonged period of exposure. This is in contrast with acute toxicity, characterized by a high level of toxicity after a single exposure. Understanding chronic toxicity is important, because substances which appear safe may actually cause the development of toxicity over time in organisms which are exposed to them.
There are two ways in which a substance can cause chronic toxicity. Some toxins work by damaging the body through a series of small exposures. A classic example is tobacco. A single cigarette is unlikely to have a toxic effect on someone, but smoking numerous cigarettes over the course of an entire lifetime will result in the development of toxicity. Other toxins work by lingering in the body. Radium, for example, will persist in the bones over an extended period of time, causing lingering health problems and chronic toxicity.
Organisms can be exposed to compounds which result in chronic toxicity in a number of ways. Many are ingested through air, water, and food products. Others may be absorbed, as in the case of compounds which emit harmful radiation that penetrates the body or compounds which can be absorbed through the skin. Someone working in a chemical plant, for example, might develop chronic toxicity as a result of not wearing the appropriate safety gear and slowly absorbing low doses of toxins over time.
Some harmful substances which cause chronic toxicity can also cause acute toxicity, if the exposure is high enough. Alcohol is an excellent example. Many of the health problems associated with alcohol consumption are the result of chronic toxicity, with the patient developing problems over time as a result of drinking regularly. However, people can also develop alcohol poisoning from drinking too much alcohol too quickly, potentially dying or becoming very ill as the result of a single exposure.
When compounds are researched to determine whether or not they are safe, a chronic toxicity study may be performed. Initial research may demonstrate that the substance does not cause acute toxicity, or that the dose required for acute toxicity is so high that it is not a cause for concern. A chronic toxicity study can reveal problems with long term exposure which may not be immediately evident in the results of shorter studies. The study of toxicity as a result of prolonged exposure is also an ongoing topic, with researchers looking for trends in the general population and seeing if they can be traced back to specific exposures.