Some aspects of target tissues in setting the annual limits on intake for non-stochastic effects

The annual limits on intake (ALI) for the radionuclides listed in Basic Health Standards for Radiation Protection (GB4792-84) were derived on the basis of stochastic on non-stochastic effects. ALIS and ALIN denote the limits based on stochastic and non-stochastic effects, respectively. Of the total number of ALI, 24% of those derived on the basis of ingestion and 11% of those based on inhalation were categorized as ALIN instead of ALIS. The organ which obtained the maximum committed dose equivalent in setting the ALIN was defined as the target organ. The target organs involved were the wall of the stomach, the wall of the lower large intestine, the bone surface, the thyroid, the liver and the kidneys. The setting of target organs related to the physico-chemical properties of the radionuclides included: chemical group, half-life, absorbed fraction and lung class. To some extent the route of intake also played a role. The ratio R(ALIS/ALIN) was selected to express the extent of decrease when ALIN was used instead of ALIS. It was shown that the values of R were related to the weighting factor of risk of ALIN target organs (WT) and the number (n) of exposed organs considered in calculating ALIS. By combining the values of individual target organs with the same WT and both routes of intake, two R-n relationship curves and the corresponding fitting equations were obtained for the values WT = 0.03 and WT = 0.06. The value of R ranged from 1.0 to 3.6 and was conditioned by WT and n. Although the extent of decrease of ALI can, in general, be neglected for target organs when using an ALIN with a value of WT = 0.06, it should be taken into account when WT = 0.03. (author). 4 refs, 5 figs, 9 tabs