Understanding The Effects Of Radiation

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If a person is exposed to radiation, especially high dose, there are predictable changes in our body that can be measured. The number of blood cells, the frequency of chromosome aberrations in the blood cells and the amount of radioactive material in urine, are examples of biomarkers that can indicate if one is exposured high dose. If you do not have early biological changes indicated by these measurements the radiation exposure will not pose an immediate threat to you.

The risk for radiation exposure has been very widely studied. The general consensus of opinion for the induction of cancer by ionizing radiation is 10% increase in cancer rate/Sv when the dose is given over a short time with a decrease to 5% when the dose is protracted over an extended time period. (one Sv is equal to 1000 mSv and one mSv is equal to 100 mRem.). Therefore a 10% increase in cancer is related to a dose of 100,000 mrem with 5% if the dose is protracted over a longer period of time.

References:NCRP National Council on Radiation Protection and Measurements, 1987, Recommendations on limits for exposure to ionizing radiation. NCRP Report No. 91 (Bethesda, National Council on Radiation Protection and Measurements).

NCRP National Council on Radiation Protection and Measurements, Risk estimates for radiation protection. NCRP Report No. 115. Issued December 31, 1993. Bethesda, Maryland. National Council on Radiation Protection and Measurements.

NCRP National Council on Radiation Protection and Measurements, 1993, Limitation of exposure to ionizing radiation. NCRP Report No. 116. National Council on Radiation Protection and Measurements, Besthesda, Maryland.

THRESHOLD FOR RADIATION INDUCED CANCER (LOW DOSE)

There is no doubt that radiation can cause cancer. The question is what level of radiation it takes to cause cancer. Some belive that this low level is about 20 rads. Below this dose it is not possible to detect adverse health effects (this level has been set by ICRP). The Health Physics Society has issued a position statement "Radiation Risk in Perspective" that addresses this issue. The statement does not claim that there are no observable health effects below 10 rem but that health risks, if they exist below 10 rem, are too small to be observed. The facts in the matter of radiation effects at low doses are very simple: no one knows whether there is any risk or not. All we can say now is that no one has detected any statistically significant effect at doses below about 100 mSv (10 rem). Some epidemiological studies suggest an increased risk of cancer in 15-20 rads dose range. However, the data suggest that risks in the 15-20 rem dose range are very small and difficult to measure. Above 10 rem there appears to be a significant risk of thyroid cancer due to radioiodine exposure in children 15 years of age and younger.
Other references: http://www.physics.umd.edu/deptinfo/facilities/lecdem/honr228q/specialtopics/LowLevRefs.htm, 

EFFECT OF A HIGH DOSE ON HUMANS AND SYMPTOMS

It is well established that high dose ionizing radiation can cause cancer. Effect/symptoms of a high dose is shown below.(Adapted from IOM/NRC, 1999a)

 0 to 25 rads:

• No easily detectable clinical effect in humans.
• However, at about 15 rads there could be temporary sterility (Testis).

25 to 100 rads:

• Slight short-term reduction in blood cells.
• Disabling sickness not common.

100 to 200 rads:

• Nausea and fatigue.
• Vomiting if dose is greater than 125 rads.
• Longer-term reduction in number of some types of blood cells.

200 to 300 rads:

• Nausea and vomiting on the first day of exposure.
• Up to a two-week latent period followed by appetite loss, general malaise, sore throat, pallor, diarrhea, and moderate emaciation.
• Recovery in about three months unless complicated by infection or injury.

300 to 600 rads:

• Nausea, vomiting, and diarrhea in first few hours.
• Up to a one-week latent period followed by loss of appetite, fever, and general malaise in the second week.
• Followed by bleeding, inflammation of mouth and throat, diarrhea, and emaciation.
• Some deaths in two to six weeks.
• Eventual death for 50% if exposure is above 450 rems.
• Others recover in about six months.

Over 600 rem:

• Nausea, vomiting, and diarrhea in the first few hours.
• Followed by rapid emaciation and death in 2^nd week.
• Eventual death of nearly 100%.

High dose could lead to death. Table below shows lethality within 24 to 48 hrs after radiation exposure without medical treatment: 

Absorbed Dose	Lethality w/o treatment, % of population, within 60 days
(rads)	Percent Lethality of population receiving absorbed dose
0 – 25	--
100 – 200	< 5.
200 – 350	< 50.
350 – 500	50 – 99
> 550	99 – 100

References:

National Council on Radiation Protection and Measurements. Oct. 2001 Management of terrorist events involving radioactive material, NCRP Report No. 138, Bethesda, Maryland.

Medical Management of Radiological Casualties, Handbook, Military Medical Operations, Armed Forces Radiobiology Research Institute, Bethesda, Maryland 20889-5603, http://www.vnh.org/MedManRadCasu/
http://hps.org/publicinformation/ate/cat66.html

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