Poison are chemical which cause illness,injury or death when taken in very small quantities. The legal definition of a poison is a chemical that takes less the 50mg per kilogram of body weight to kill 50% of the victims exposed. This is really a very small amount of material - about 3/4 of a teaspoon for the average adult and about 1/8 a teaspoon for a 2 year old child. There are very few chemicals that are lethal at these doses, but those that are must be classified as poisons. These materials will be classified as "acute poison" because their effect is immediate.
Chronic toxicity, on the other hand, refers to the systemic damage that is done after repeated exposure of low concentrations over long periods of time. Materials most often associated with chronic toxicity are those that have been labeled as carcinogens, though there are other classes of chronic toxins which must be used with equal care. All chronically toxic materials are problematic because we do not know when or if the effect of the exposure will be felt. Workers in research laboratories and in other chemical settings should not discount any chemical exposure - materials not thought to be hazardous in the recent past are often found to be carcinogenic at a later time.
Most chemicals exhibit some degree of both acute toxicity and chronic toxicity. The symptoms displayed and the systemic effect will, however, differ. In addition, some materials may act as chronically toxic, but show no chronic ill effects. The same is true for materials labeled as chronically toxic, which have no adverse single dose effect. Despite this lack of correlation, the effects of both forms of toxicity are definitely dose related, that is, the greated the dose, the greater the effect.
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