Why are exposure and dose important?
“The dose makes the poison” About 500 years ago, the scientist Paracelsus said, “…nothing is without poisonous qualities. It is only the dose that makes the poison.” Large amounts of a relatively harmless substance can be toxic. Two aspirin can relieve a headache, but taking an entire bottle of aspirin can cause vomiting, convulsions or death. The dose is the amount of a substance that enters or contacts a person. Exposure is the way something enters an organism (i.e., by eating, drinking or absorption through the skin). Arsenic is very widely distributed in the environment and all humans are exposed to low levels of this element in food, water and air. For most people, food and water are the largest source of exposure to arsenic. Much lower amounts come from air and soil. These would even be lower under typical residential conditions where soils are covered with grass. (Borum and Abernathy 1994, Hughs and Meek 1994) The presence of a substance doesn’t tell us whether people are expo
