Two Aspects of Non-Linear, Non-Threshold Response Deleterious Effect Illustrative Types of Response Curves Dose It is easy to add additional charts to these curves, and I have done that on purpose in the ones that have been presented. The space F shows an additional chart labeled L which is put on in a few minutes with tape and shows a particular case of a linear response which also has a threshold. In other words, it shows a straight line not passing through the origin. Mr. RAMEY. Chart E shows that it goes below and appears beneficial at certain dosages. Mr. PARKER. When one looks at the data there are a surprising number of experiments in which at least this illusion is given, and I am sure that witnesses later in the week will refer to this effect. So a negative deleterious effect in this sense is printed on the chart as a beneficial effect at very low dose. Until the resolution as to which of these curves applies in any and all cases prudent men must make the safe assumption that some kind of nonthreshold response applies. Ultimate safety in the extremist sense then requires no radiation exposure, and, consequently, no use of radiation. In practical terms, one accepts a risk principle to balance potential detrimental effect against potential benefit of radiation use. Two additional balances are implicitly involved here. The first is a balance of the authoritative voices trying to define the optimum point. The second is an obligation to balance the effort that goes into the radiation protection case against that which should go into parallel treatments of all the other agents or influences (for example, chemicals) that may have comparable effects on our national life, projected over an indefinite number of generations. In the remaining time I would like to have pages 6 through 12 of the preprint material considered as part of this presentation. Here I will just briefly highlight some of this material. Present-day standards for protection of individuals against radiation depend substantially on recommendations of the National Committee on Radiation Protection and the International Commission on Radiological Protection. Mostly these have been concerned with prevention of injury to occupational workers. More recently the much broader questions of exposure to groups not susceptible to special medical examinations and including young children and old or infirm people were considered. Separate treatments of permissible dose to populations with respect to genetic effects and somatic effects have appeared. NCRP and ICRP recommendations are in two parts: 1. Basic permissible dose limits, including specific limits for the whole body or for specified critical organs; derived maximum permissible body burdens of various radioactive materials, usually as calculated to give the limiting radiation dose; derived maximum permissible concentrations of these materials in drinking water or air, calculated to lead to maximum permissible body burdens. All these will be modified according to whether the application is restricted. to occupational workers or not. 2. Recommended practices: Numerous handbooks provide information on methods of doing work with radiation-emitting sources or equipment that will facilitate responsiveness to the basic limits. The preprint identifies six sources of exposure to be considered. My table I (p. 17) lists estimated background radiation from various published sources. Similar data may be used by a number of witnesses. I would respectfully suggest, Mr. Chairman, that confusion could be avoided and time saved if witnesses planning to use background radiation doses could meet with a member of your staff to produce one table to which all of us could agree. The data shown today are smoothed off compared with the preprint material with this in mind. An outright error that crept into the potassium 40 figures in the somewhat hasty preparation is also corrected. Let me make two observations about natural background. First, it does vary from place to place. Attempts to fix it by fiat at any arbitrary dose level obscure rather than clarify the picture. In the second place, background radiation is generally excluded from radiation protection limits because nothing can be done about it. Actually, we have been considering some experiments in which we can support animals at only 1 percent of the natural background, so something can be done about it if need be. Also, if we contemplate average annual population doses of the order of 100 millirem per year, the question of whether one lives in a wooden, brick, or concrete house may not be wholly irrelevant as suggested by the Swedish data. It may even be fair to ask whether living in any kind of a house is "natural," and, hence, whether the house-originated component of radiation should be included in "natural background." In the field of medical exposure, estimates of dose from diagnostic and therapeutic procedures cover the range from 1.5 to 5 roentgens per person in 30 years. This constitutes about 99 percent of the manmade radiation contribution at the present time. Criteria for control of medical irradiation rest on the welfare of individual patients with the physician exercising value judgment as the controlling factor. This tends to set medical exposure standards apart from any other, a procedure that is acceptable provided that physicians using radiation consciously assume the obligation to include evaluation of this type of risk within their professional competence. In the field of occupational exposure, the total contribution to the Nation's burden of genetically significant dose is quite modest. The relevant criterion is the probability of somatic damage to exposed individuals. The preprint draws attention to one concrete example-accidental overexposure in the State of New York, in which the contribution. from conventional radiation sources in no way related to atomic energy programs is quite significant. The intent is to suggest that perspective concerning the exposure contribution by atomic energy programs as a fraction of the total exposure needs to be maintained or perhaps restored. The field of population exposure will properly receive much attention during these hearings. Table III (p. 18) reports conventional estimates of the various contributions to population dose in the United States. As for table I, it would be helpful if some simple modification of this could be accepted throughout the hearings. Some special considerations applying to population dose are given in note form: (a) Authority of knowledge to define limits differs from that for occupational dose; |