When humans are exposed to low doses of radiation, it is difficult to estimate what small increment of mutations is induced by radiation above that from spontaneous background radiation. The mutations induced by radiation can also occur spontaneously. Moreover, for risk estimation of exposures that are not uniformly or randomly delivered to the entire population, the age and sex distribution of the exposed population and the different probabilities of having children for members of the population of each age and sex must be taken into account. The time lag is great because of the duration of the human life cycle, and massive epidemiologic studies with long-term follow-up are needed to accumulate sufficient data for statistical analysis. The genetic effects of radiation are expressed, not in irradiated individuals, but in their immediate or remote offspring. The following are some of the difficulties and considerations that must be kept in mind. This is why, more than 20 years after the BEAR Committee first addressed the issues of radiation exposure, there is still uncertainty and controversy. There are many difficulties in measuring the genetic effects of exposure of the human population to radiation and other mutagens.
Despite changed conditions, estimating the genetic effects of radiation remains important for setting exposure standards, both for the general population and for those exposed in their occupations. Third, in regard to the induction of mutations, the greater current risk seems to result from exposure to chemical mutagens in the environment rather than from the exposure of populations to radiation.
Second, the instruments and techniques used in medical radiation have improved significantly, so that the overall doses used in medical diagnoses are reduced and patient exposure in all but the targeted organs is lessened.
First, it is now clear that the risk of cancer in individuals exposed to radiation is significant and that limiting exposure to radiation to reduce the risk of cancer also limits the genetically significant exposure. Scientific Committee on the Effects of Atomic Radiation ( UNSCEAR) has also addressed the genetic effects of radiation exposure on populations.Īlthough there is a continuing need to assess the genetic effects of radiation exposure, for several reasons the perspective has changed somewhat from that in the 1950s. In 1956 the National Academy of Sciences-National Research Council (NAS-NRC) established the Committee on the Biological Effects of Atomic Radiation (denoted the BEAR Committee), which was the forerunner of the subsequent NAS-NRC committees on the Biological Effects of Ionizing Radiation (BEIR committees of which this BEIR V report is one). These efforts were motivated by concern over the effects of extremely large sources of radiation that were being developed in the nuclear industry, of radioactive fallout from the atmospheric testing of atomic weapons and of the rapidly increasing use of radiation in medical diagnosis and therapy. Although occupational exposure to high levels of radiation has always been of concern, not until during and after World War II was there a concerted effort to evaluate the genetic effects of radiation on entire populations. The mutagenic effects of radiation were first recognized in the 1920s, and since that time radiation has been used in genetic research as an important means of obtaining new mutations in experimental organisms. Ionizing radiation damages the genetic material in reproductive cells and results in mutations that are transmitted from generation to generation.
0 kommentar(er)
