Id... be about fivefold larger. Added to these would be a smaller number caused by chromosomal defects and recessive diseases. (c) Risk Relative to Current Prevalence of Serious Disabilities. In addition to those in (b) caused bysingle-gene defects and chromosome aberrations are con- genital abnormalities and constitutional] diseases Which are partly genetic. It is estimated that the tota]incidence from all these including those in (b) above, would be between 1100 and 27,000 per vear at equilibrium (again, based on 3.6 million births). This would be about 0.75% at equilibrium, or 0.1% in the first generation. (d) The Risk in Terms of Overall Il]-Health. The most tangible measure of total genetic damage is probably “ill-health” which includes but is not limited to the above categories. It is thought that between 5% and 50% of ill-health is proportional to the mutation rate. Using a value of 20% anda doubling dose of 20 rem, we can calculate that 5 rem per generation would eventually lead to an increase of 5% in the illhealth of the population. Using estimates of the financial costs of i]]-health, such effects can be measured in dollars if this is needed for costbenefit analysis. Until recently, it has been taken for granted that genetic risks from exposure of populations to ionizing radiation near background levels were of much greater import than were somatic risks. However, this assumption can no longer be made if linear non-threshold relationships are accepted as a basis for estimating cancer risks. Based on knowledge of mechanisms (admittedly incomplete) it must be stated that tumor induction us a result cf radiation injury to one or a fewcells of the body cannot be excluded. Risk estimates have been made based on this premise and using linear extrapolation from the data from the A-bomb survivors of Hiroshima and Nagasaki, from certain groups of patients irradiated therapeutically, and from groups occupationally exposed. Such calculations based on these data from irradiated humans lead to the prediction that additional exposure of the U.S. population of 5 rem per 380 years could cause from rough]. 3,000 to 15,000 cancer aeat: - annually, depending on the assumptions used in the calculations. The Committee considers the most likely estimate to be approximately 6,000 cancer deaths an- nually, an increase of about 2% in the spontaneous cancer death rate which is an increase of ee | sip about 0.8% in the overal]! death rate from a. causes. Given the estimates for genetic and somat:: risk, the question arises as to howthis infc:mation can be used as a basis for radiatic: protection guidance. Logically the guidance o: standards should be related to risk. Whethe: we regard a risk as acceptable or not depencon how avoidable it is, and, to the extent me: avoidable. how it compares with the risks of alternative options and those normally accepted by society. There is reason to expect that over the nex: few decades, the dose commitments for al! manmade sources of radiation except medicé. should not exceed more than a few millirems average annual dose to the entire U.S. population. The present guides of 170 mrem/yr grew out of an effort to balance societal needs against genetic risks. It appears that thes needs can be met with far lower average expesures and lower genetic and somatic risk then permitted by the current Radiation Protecticr: Guide. To this extent, the current Guide is ur necessarily high. The exposures from medical and dental uses should be subject to the same rationale. To the extent that such exposures can be reduced without impairing benefits, they are also un- necessarily high. It is not within the scope of this Committee ta propose numerical limits of radiation exposure. It is apparent that sound decisions require technical, economic and sociological considera- tions of a complex nature. However, we can state some general principles, many of which are well-recognized and in use, and some of which mayrepresent a departure from present practice. a) No exposure to ionizing radiation should be permitted without the expectation of a commensurate benefit. b) The public must be protected from radiation but not to the extent that the degree of protection provided results in the substitution of a worse hazard for the radia- tion avoided. Additionally there should not be attempted the reduction of small risks even further at the cost of large sums of money that spent otherwise. would clearly produce greater benefit.