Some aspects of target organs in setting annual limits on intake of radionuclides for non-stochastic effects

The Annual Limits on Intake (ALI) of radionuclides listed in 'Basic Health Standards for Radiation Protection' (GB4792-84) were derived on the basis of stochastic or non-stochastic effects. It was supposed that ALIS meant the limits based on stochastic effects, and ALIN on nonstochastic ones. Under ingestion mode, ALIN amounts to 24 percent of ALI and 11% under inhalation mode. The organ which obtained the maximum committed dose equivalent in setting ALIN was defined as ALIN target organ. The AILN target organs involved in setting all ALIN were wall of stomach, wall of lower large intestine, bone surfaces, thyroid, liver and kidney. Setting of target organs is related to physical-chemical characters of radionuclides, including the family in which they are, half-life, fractional absorption, and inhalation class. The route of intake played the role in some extent. The ratio R (ALIS/ALIN) was selected to express the extent of decressing for ALI as ALIN was used as the ALI instead of ALIS. It was showed that the values of R is related to weighting factor of risk of ALIN target organs (WT) and the number of exposed organs considered in calculating ALIS (n). Combining the values of individual ALIN target organs with same WT and both routes of intake, two R-n relationship curves and corresponding fitting equations could be obtained for WT=0.03 and WT=0.06 groups, respectively. The R ranged from 1.0 to 3.6 conditioned by the WT and n. Using the ALIN, the extent of decrease of ALI might be neglected as a whole for the ALIN target organs with WT=0.06; but it should be payed attention to that with WT=0.03