PTWI stands for Provisional Tolerable Weekly Intake. It describes the amount of a substance that can be eaten every week throughout a person`s life with no risk of negative health effects. Use of the word ”provisional” means that the assessment is temporary and that it will be reconsidered when more data is available. An assessment of this kind will always include a certain safety margin.  Consuming more than the PTWI limit does not pose an immediate health risk, but the safety margin is reduced.