Delayed effects, radiation

The reader should note tliat since many risk assessments have been conducted on the basis of fatal effects, there are also uncertainties on precisely what constitutes a fatal dose of thennal radiation, blast effect, or a toxic chemical. Where it is desired to estimate injuries as well as fatalities, tlie consequence calculation can be repeated using lower intensities of exposure leading to injury rather titan dcatli. In addition, if the adverse healtli effect (e.g. associated with a chemical release) is delayed, the cause may not be obvious. Tliis applies to both chronic and acute emissions and exposures. 

B.4.3.2 Delayed Effects. The level of exposure to radioactive pollutants that may be encountered in the environment is expected to be too low to result in the acute effects described above. When one is exposed to radiation in the environment, the amount of radiation absorbed is more likely to produce long-term effects, which manifest themselves years after the original exposure, and may be due to a single large over-exposure or continuing low-level exposure. 

Three more National Research Council committees (the first, second, and third Committees on the Biological Effects of Ionizing Radiations—BEIR I, II, and III) issued reports in 1972, 1977, and 1980.301-303 They emphasized risk estimation, rather than recommendation of standards. There also has been discussion of carcinogenicity as a low-dose, delayed effect. The United Nations, through its Scientific Committee on the Effects of Atomic Radiation, has continued to produce periodic encyclopedic reviews of the literature.1+68-473... 

The dangers associated with ionizing radiation, or with cigarette smoking, should have sensitized the public as well as scientists to the importance of delayed effects. But, surprisingly, this knowledge has not increased awareness of the fact that most other technological innovations also have delayed effects. 

Fig. 2. Radiation damping effects on water longitudinal relaxation versus the t delay in an inversion recovery sequence (i.e. 7r-T-7r/2-Acq.) in a lysozyme sample (10 mM in 10 90 H20 H20, pH 3.7) at room temperature at 300 MHz using a 5mM inverse...

Radiation damage may also occur from exposure to the skin. Medically, radioactive strontium probes have been used intentionally to destroy unwanted tissue on the surface of the eye or skin. The eye tissues sometimes become inflamed or abnormally thin after a long time. Thinning of the lower layer of the skin (dermis) has also been reported in animal studies as a delayed effect. In addition, skin and bone cancer were reported in animals that were irradiated on the skin by exposure to a radioactive strontium probe. 

Mancuso T, Stewart A, Kneale G. 1981. Analyses of Hanford data Delayed effects of small doses of radiation delivered at slow-dose rates. In Peto R, Schneiderman M, eds. Quantification of occupational cancer. Banbury report 9. Cold Spring Harbor, Ml Cold Spring Harbor Laboratory, 129-150. 

Not aU delayed effects are due to low levels of exposure. The onset of cancer which may occur due to e q)osure to asbestos or radiation is often delayed for periods of 15 or more years, or, and this is a key point, they may not occur at all. By no means do all individuals exposed to even high levels of such hazards suffer the consequences. 

The answers we found responded to grave questions about the short-term effects of radiation, including the toll of fallout. The answers that continued to elude us had to do with the long-term genetic consequences. And we are still accumulating data on the delayed effects represented by some cancers appearing only as the survivors reach old age. 

As I planned my return to Nagasaki in 1989, I felt substantial satisfaction in the progress made during the past forty years in understanding the short-term effects and some of the delayed effects of radiation among the survivors. But all of us who participated in the radiation research were perplexed about the absence of a clearer understanding of the genetic impact. 

In general, to assess the delayed effects of current exposure, dose quantities of the ionizing radiations are introduced. The term dose is used in a general sense as a measure of the quantity of radiation or the energy deposited by radiation in a target. For the strictest use in dosimetry, the term must be specified as absorbed dose, equivalent dose, organ dose, etc. These quantities may refer to exposed individuals (individual dose) or to a group of people (collective dose). 

Ethanol and methylmethacrylate injections may be performed together if both weight-bearing and non-weight-bearing bones are involved or extensive soft-tissue involvement is present. Moreover, these injections may be performed prior to radiation therapy, which complements their action due to similar but delayed effects on pain, or after unsuccessful pain relief by radiation therapy, or in cases of local recurrence. 

Much of the early work on chemical radiation protection has been reviewed in the books by Thomson [415] and Bacq [416]. Many of the substances which have potential value in this area have a fairly high toxicity and the differences between the toxic and protective doses are often quite small. Much of the research that has been carried out so far has been concerned with protection against acute lethality however, relatively little work has been reported, until quite recently, on protection against delayed effects and sublethal damage. 

Figure 2 Analysis of the cell cycle effect of radiation on human fibroblast cells pulse labelled with BrdUrd. (A) Representative isometric displays of DNA content (x axis) versus BrdUrd uptake (y axis) versus cell number (z axis) are presented for irradiated and control cell cultures. (B) The DNA profile of the BrdUrd labelled cells at 10 hours has been gated. The solid fill represents the control cells which has been overlaid with the histogram from the Irradiated cells. (C) A plot of entry of labelled cells into Gl (region 1 In B) displays the division delay effect of radiation (A) compared to control cultures (0).

After apparent recovery from an acute radiation exposure, an individual may experience a delayed effect as a result of this acute exposure. However, there is also evidence that chronic low-level radiation exposures can also result in delayed effects. Little is known about the etiology of these effects, or if any threshold exposures exist below which delayed effects do not occur, so this is an area of real concern to those who work with radioactive substances on a regular basis. Table 13.3 gives estimates of the risks to humans of various delayed effects of exposure to low-level radiation. Let us briefly look at some of these delayed effects of radiation exposure. 

Table 13.3 Probability of delayed effects from low-level radiation exposure...

S. Nagataki. Delayed effects of atomic bomb radiation on the thyroid, in "Radiation and the Thyroid", S. Nagataki,ed., Excerpta Medica, Tokyo (1989)... 

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