Each of us is concerned to some degree about the effects of chemicals on people, animals, and the environment. We are also aware of environmental contaminants that affect public health, such as the effects on our children of lead in soil and drinking water. This is the business of toxicology .
Any substance can be toxic.
The higher the exposure to any substance, the greater the chance of an adverse effect. One example is sodium chloride, or table salt. Although essential to life, children have died from eating salt and many adults suffer from hypertension, which is associated with too much salt in the diet. A number of vitamins are toxic at high doses. Vitamin D, in fact, is classed as a highly toxic substance and only tiny amounts are needed for proper nutrition.