amount of a chemical to which a person can be exposed each day for a lifetime. The EPA and ATSDR calculate Reference Doses or Minimal Risk Levels for noncancer end points which are similar in concept to ADIs. Animal doses must be converted to human dose equivalents to account for differences in body size and physiology. Historically, FDA used a simple ratio of body weights whereas EPA used a ratio of surface areas to calculate the human dose equivalent. Both have agreed to use the body weight ratio raised to the 3/4th power