- 18 - Cc. ‘The Hot Particle Problem It is important to recognize that the ICRP has given -mo guidance with respect to nonuniform irradiation of the lung by insoluble alpha-emitters such as insoluble plutonium particles. In its Publication 9, the ICRP states: ~..In the meantime there is no clear evidence to show whether, with a given mean absorbed dose, the biological risk associated with a non-homogeneous distribution is ‘ greater or less than the risk resulting from a more diffuse distribution of that dose in the lung. 29 In effect, the ICRP is saying that there is no guidance as to the risk for non-homogeneous exposure in the lung, hence the MPC, and the MPLB are meaningless for insoluble plutonium particles. The NCRP offers the following and similar statement with: respect’ to these particles: (210) The NCRP has arbitrarily used 10 percent of the volume of the organ as the significant volume for irradiation of the gonads. There are some cases in which che+ce of a significant volume or area is virtually meaningless. For example, if a single particle of radioactive material fixed in either lung or lymph noce may be carcinogenic, the averaging of dose either over the lung cr even over one cubic centimeter may have little to do with this case. 2° This hot particle problem is also-well .recognized in: the biological community. The following is extracted froma 29/ ICRP Publication 9, Op. cit., p. 4. 30/ NCRP Report No. 39, Op. cit., pp. 79-80.