Chronic toxicity Much of the knowledge we have about chronic toxicity comes from animal experiments. In addition, much has been learned from studying groups of people occupationally exposed to a chemical for many years. As a general rule, chronic toxicity appears many years after exposure first began. The resulting disease occurs only because the exposure has taken place repeatedly over many years. Chronic toxicity diseases do not seem to be caused by sudden one-time exposures.
Chronic toxicity is thought to occur in one of two main ways.
These can be explained by using sodium fluoride and n-hexane as examples. Indeed, at these low levels, the effects are considered beneficial for teeth. However, if much higher concentrations of sodium fluoride enter the body repeatedly, they deposit and build up in the bones. At first, the amount of fluoride in the bone may not cause any problems, but after years of repeated high exposure, symptoms of bone disease may appear. On the other hand, the chemical n-hexane is not deposited or accumulated in the body.