The acute toxicity of a chemical refers to its ability to do harm as a result of a one-time exposure to the chemical. This exposure is sudden and commonly produces a health emergency. Chronic toxicity, by contrast, refers to the ability of a chemical to do systematic damage as a result of repeated exposures to small quantities or low concentrations of a chemical over long periods of time. The reactions produced by these two different types of exposure bear no resemblance to one another. The chronic toxic effects of a chemical cannot be predicted from knowledge of that chemical's acute exposure effects.
Some chemicals have a high acute toxicity but no chronic toxicity.
That is to say, small quantities over a long period of time are harmless and, in some cases, are beneficial. Vitamin D and fluoride are two examples. We require small quantities of vitamin D daily for good health, and we know that fluoride is essential for good dental health. The same can be said of sodium chloride, common table salt. Not surprisingly, some chemicals are chronically toxic but acutely non-toxic.