Radiation exposure, health effects

Nonstochastic (nonrandom) radiation-induced health effects can be prevented by limiting exposure so that doses are below the thresholds for their induction. 

Radiation exposures can effect the health of exposed individuals. The type of effect, its severity, and the length of time until the effect appears are determined by the total dose received, the rate of exposure, and the exposed organs, and the degree of medical treatment received. 

Most of the data on radiation health effects have come from medical monitoring of Japanese atomic bomb survivors. For survivors who received radiation exposures up to 0.10 Sv, the iacidence of cancer is no greater than ia the geaeral populatioa of Japanese citizens. For the approximately 1000 survivors who received the highest radiation doses, ie, >2 Sv, there have been 162 cases of cancer. About 70 cases would have been expected ia that populatioa from aatural causes. Of the approximately 76,000 survivors, as of 1995 there have beea a total of about 6,000 cases of cancer, only about 340 more cases than would be expected ia a group of 76,000 Japanese citizens who received only background radiation exposure (59). 

For radiation doses <0.5 Sv, there is no clinically observable iacrease ia the number of cancers above those that occur naturally (57). There are two risk hypotheses the linear and the nonlinear. The former implies that as the radiation dose decreases, the risk of cancer goes down at roughly the same rate. The latter suggests that risk of cancer actually falls much faster as radiation exposure declines. Because risk of cancer and other health effects is quite low at low radiation doses, the iacidence of cancer cannot clearly be ascribed to occupational radiation exposure. Thus, the regulations have adopted the more conservative or restrictive approach, ie, the linear hypothesis. Whereas nuclear iadustry workers are allowed to receive up to 0.05 Sv/yr, the ALARA practices result ia much lower actual radiatioa exposure. 

Health Effects Of Exposure to Row Revels oflonifing Radiation, Report of Committee on the Biological Effects of Radiation (BEIR Report V), National... 

In terms of health effects, none of the evacuees from the 30 km radius evacuation zone displayed any symptoms of radiation sickness. Their collective dose from external exposure wa.s estimated to be 1.5... 

The nuclear explosions that devastated Hiroshima and Nagasaki killed 100,000 to 200,000 people instantaneously. Probably an equal number died later, victims of the radiation released in those explosions. Millions of people were exposed to the radioactivity released by the accident at the Chernobyl nuclear power plant. The full health effects of that accident may never be known, but 31 people died of radiation sickness within a few weeks of the accident, and more than 2000 people have developed thyroid cancer through exposure to radioactive iodine released in the accident. Even low levels of radiation can cause health problems. For this reason, workers in facilities that use radioisotopes monitor their exposure to radiation continually, and they must be rotated to other duties if their total exposure exceeds prescribed levels. 

The radiation from exposure to americium is the primary cause of adverse health effects from absorbed americium. Upon entering the body by any route of exposure, americium moves relatively rapidly through the body and is concentrated in bones where it remains for a long time. While in the bone, americium atoms decay, releasing alpha particles and gamma-rays. Alpha... 

Epidemiological and Human Dosimetry Studies. Epidemiological studies of radiation dose typically involve estimates of exposure that are based on whole-body measurements of internally-deposited americium. A need remains for epidemiological data that can provide quantitative human dose-response information while supplying additional information on the health effects of exposure to ionizing radiation and americium in particular, for cases of known internal exposure. 

BEIRV. 1988. Health effects of exposure to low levels of ionizing radiation. Committee on the Biological Effects of Ionizing Radiations, National Research Council. Washington, DC National Academy Press. 

It should be noted that there is intense controversy as to the health effects of radiation doses below about 100 mSv per year. This estimate of 15,000 annual cancer deaths from indoor radon, as well as estimates of tens of thousands of eventual cancer deaths from Chernobyl exposures, is obtained by applying the linearity hypothesis. This hypothesis has been adopted by most regulatory agencies but is strongly contested by some scientists who believe it overestimates the effects of radiation at low dose levels. Of course, if calculations based on this hypothesis overestimate the deaths from indoor radon, they also overestimate the effects of potential radiation from a waste repository. 

For comparison, the health effects calculated from exposure to natural background radiation levels for typical residential properties were all about 0.01 per property, with radon daughters accounting for more than 50% of the total health effects estimated. 

Marks, S., F.T. Cross, D.H. Denham, and W.E. Kennedy Jr., Estimation of Health Effects due to Elevated Radiation Exposure Levels in Structures, Sci. Total Environ. 45 543-550 (1985b). 

Radiation dose Level of exposure to radiation, expressed in units called Roentgen equivalents in man (rem) a dose of approximately 400 rem is fatal in 50% of cases when medical treatment is not available. No health effects are typically observed at doses below 10 rem. 

Long-term health effects from exposure to low-to-moderate doses of radiation include cancer of the thyroid, prostate, kidney, liver, salivary glands, and lungs Hodgkin s disease leukemia and increased numbers of stillbirths and genetic defects. Concerns about potential long-term health effects often lead to anxiety and depression problems among those exposed to radiation. 

Radioactivity results when some part of an atom is unstable. The instability exists because the orbital electrons or the nucleus contain too much energy. Radioactive atoms are called radionuclides. They release excess energy by emitting radiation. The type of radiation released (alpha, beta, or gamma particles) may be more or less hazardous to humans, depending on the location of the radioactive materials. Exposure to radioactive materials outside the body poses external hazards. Radioactive materials may also be hazardous when ingested, inhaled, or injected and thus pose internal hazards. The sections below describe the characteristics of radiation particles as external or internal hazards and as they may be encountered after a terrorist attack. Chapter 3 provides additional details and addresses health effects associated with exposure to radiation. 

Dose" as defined here refers to the absorption of radiation energy by human tissue. Higher doses correspond to higher potential for adverse health effects, as described in Chapter 3. The terms dose and exposure are often used interchangeably. 

Health effects from exposure to radiation fall into two categories stochastic (based on probability) and acute. Stochastic effects typically take several years to materialize (e.g., cancer appearing 20 years after an exposure) while acute effects such as nausea or reddening of the skin may take only weeks, days, or even hours to materialize. Stochastic and acute effects are described in more detail in the following sections. First, however, a brief discussion describes how radiation damages human tissue and why exposure may produce one or a combination of the described health effects. 

Stochastic radiation effects are typically associated with those that occur over many months or years (i.e., are typically chronic instead of acute). Chronic doses are typically on the order of background doses (0.3 rem [0.003 Sv] or less) and are not necessarily associated with larger doses that could result from a terrorist attack with radiological weapons. However, stochastic health effects are defined here as effects that occur many years after chronic or acute exposure to radiological contaminants. Stochastic effects are categorized as cancers and hereditary effects. Because no case of hereditary effects (e.g., mutation of future generations) has been documented, this discussion focuses on cancer risk. 

Specific health effects resulting from an acute dose appear only after the victim exceeds a dose threshold. That is, the health effect will not occur if doses are below the threshold. (Note that this is significantly different from the LNT model used to predict stochastic effects.) After reaching the acute dose threshold, a receptor can experience symptoms of radiation sickness, also called acute radiation syndrome. As shown in Table 3.2, the severity of the symptoms increases with dose, ranging from mild nausea starting around 25-35 rad (0.25-0.35 Gy) to death at doses that reach 300-400 rad (3-4 Gy). Table 3.2 shows that the range of health effects varies by both total dose and time after exposure. 

The response to a nuclear explosion differs dramatically from the response to an attack with conventional explosives. When conventional explosives such as dirty bombs disperse radiological materials, the health hazards from the radiation exposure are secondary to the explosion (flying shrapnel, debris, fire, and smoke). In the case of a nuclear explosion, the risks of death, serious short-term health effects, and serious long-term health effects are no longer secondary to the explosion. 

Radioactive substances (radionuclides) are known health hazards that emit energetic waves and/or particles that can cause both carcinogenic and noncarcinogenic health effects. Radionuclides pose unique threats to source water supplies and chemical processing, storage, or distribution systems because radiation emitted from radionuclides in chemical or industrial waste systems can affect individuals through several pathways by direct contact with, ingestion or inhalation of, or external exposure to, the contaminated waste stream. While radiation can occur naturally in some cases due to the decay of some minerals, intentional and nonintentional releases of... 

This site contains information on health effects and emergency response to radiation exposure. 

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