The concepts of critical organ and radiation dose as applied to plutonium

The concepts of critical organ or tissue and the calculation of radiation dose have been and may well continue to be central to the development of standards for most radionuclides. In the case of plutonium the occupational standard was based on a modification of the direct calculations of maximum permissible annual dose (MPAD) or dose rate but critical organs must still be chosen for different routes of entry and different compounds and for all of the derived standards. Changes in such standards by likely variations in metabolic parameters and models are shown to be significant but not large. Application of the critical organ concept to population exposure standards poses some new problems because the basic MPAD does not distinguish among organs. A simple scaling factor from occupational exposure standards thus is not satisfactory. Use of the concept of dose commitment has many advantages but it is still necessary to select a critical organ and calculate dose. By-passing some of the problems in present practices by using risk-estimates seems unlikely for plutonium at the present time because of the paucity of human effects data and the fact that the animal experiments used quite different dosage regimens from the likely exposure situations to plutonium. A brief comparison is made of radiation and chemical hazard evaluation procedures.