IEER SDA Volume 4, Number 1

A Special Centerfold for Techno-Weenies

A Tool Kit on Natural and Man-made Radiation:
Tables

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Natural Radionuclide Concentration in Soils
RadionuclideAverage (pCi/g)Range(pCi/g) Comments
Natural Uranium(1)about 20.2 - 7.6Uranium ore at 0.2% concentration is 1300 pCi/g. About one half of the radioactivity is from uranium-238, about one half is uranium-234, and only a small amount is due to uranium-235.
Natural Thorium-2321about 1.00.1 - 3.5-
Natural Radium-226about 1.00.2 - 4.3-
Carbon-14 in plants and animals 6 pCi of carbon-14 per gram of total carbon2--
Potassium-40about 10--
Rubidium-87 about 1.4--
Sources: Myrick et al. 1983; Eisenbud 1987; NCRP 1987.

1. The Nuclear Regulatory Commission (NRC) has published draft radiological criteria for the decommissioning of licensed facilities. Under present clean-up guidelines, written in 1981, the NRC uses a maximum allowed concentration of natural uranium and natural thorium for surface contamination of soil of 10 pCi/g.
2. Most carbon is carbon-12, the non-radioactive isotope of carbon that forms the foundation of living matter.

Natural Radionuclide Concentrations in Continental Waters
RadionuclideSurface water (pCi/liter)Ground water (pCi/liter)Notes
Uraniumabout 1 about 3-
Radium-22630.1 - 0.50.5 - 1004EPA standard for radium-226 in drinking water is 5 pCi/liter5
Radon-2226> 1.0100 - 1,000The EPA proposed standard for radon in drinking water is 300 picocuries/liter. Some areas of Maine have very high concentrations, where the mean concentration 24,000 pCi/l
Tritium (H3)5.4 - 24.3--
Sources: UNSCEAR 1993; UNSCEAR 1982; NCRP 1988; NCRP 1984; Eisenbud 1987.

3. The radium content of surface waters is low. In the U.S., three-fourths of the population uses surface water as its drinking water supply. Measurements for average natural radium-226 activity in groundwater, however, have been sparse because water with a gross alpha activity of less than 5 pCi/l is not normally investigated for radium activity. Daily consumption of 2 liters of water containing 25 pCi/l of radium-226 would give an annual dose to the bone of 1 rem. The EPA organ dose limit for bones and all other organs except the thyroid is 0.025 rem (25 millirem) per year.

4. Some drinking water supplies in many areas exceed the limit of 5 picocuries per liter of radium-226; some have concentrations as high as 25 picocuries per liter.

5. Under the Safe Drinking Water Act (Public Law 93-523), water whose total alpha activity is more than 5 picocuries per liter has to be analyzed for radium-226 activity. If this activity is more than 3 picocuries per liter, the water has then to be tested for radium-228 as well.

6. Radon concentrations in groundwater, including some used for potable water supplies, can be very high, up to several thousand and even several tens of thousands of picocuries per liter. However, the ranges vary a great deal. Measurements of radon in drinking water have tended to be taken in areas with high levels. There is no comprehensive survey that has determined a reliable average concentration figure for radon in groundwater used for domestic water supply.

Radionuclide Deposition Due to Fallout from Atmospheric Testing
RadionuclideConcentration (picocuries/gram) Comments
Tritium in water during peak fallout periodseveral thousand picocuries/litermostly decayed away by the 1990s
Krypton-85 in air from fallout and plutonium production in 19700.01 picocuries/liter-
Plutonium-239 in soil
Northern hemisphere
Northern hemisphere 40-50o		-
0.04
0.06		-
Plutonium-241 in soil
Northern hemisphere
Northern hemisphere 40-50o		-
0.80
1.23 		-
Plutonium-240 in soil
Northern hemisphere
Northern hemisphere 40-50o		-
0.02
0.04		-
Cesium-137 in soil
Northern hemisphere
Northern hemisphere 40-50o		-
5.7
8.8		Figures are for original deposition
Over half has decayed away.
Strontium-90 in soil
Northern hemisphere
Northern hemisphere 40-50o		-
3.6
5.5		Figures are for original deposition
Over half has decayed away.
Sources: UNSCEAR 1993; Eisenbud 1987.

Typical Estimated Annual Effective Dose Equivalent7 From Natural Sources
Source Effective dose equivalent (millirem/year)
ExternalInternalTotal
Cosmic rays (including neutrons)30-30
Cosmogenic nuclides (Mainly carbon-14)-1.51.5
Primordial nuclides
potassium-40
rubidium-87		-
12
-		-
18
0.6		-
30
0.6
Uranium-238 series
uranium-238
thorium-230
radium-226		-
9
-
-		-
1.0
0.7
0.7		-
10
0.7
0.7
thorium-232141.615.6
Total (rounded)652489
Source: Eisenbud 1987.

7. "Effective Dose Equivalent" refers to the equivalent dose to the whole body received by a person. It is calculated by assigning factors to convert radiation dose to specific organs, such as bone or lung, to equivalent whole body dose. The "totals" section of the table shows that each person typically receives about 89 millirem per year from natural sources of radiation at sea level.

Natural Radiation from Outdoor and Indoor Radon-222
SourceAverage concentration (picocuries/liter)Typical range (picocuries/liter)
Outdoor concentration 0.27 0.1 - 0.4
Indoor concentration 1.10 0.3 - 88
Unventilated uranium mines-- 1,000 - 100,000
Caves-- 10 - 300
Source: NCRP 1988; UNSCEAR 1993.

8. In some areas and homes the concentration of radon-222 can be much higher, as high as 100 pCi/l or more. It is estimated that 10,000 pCi/l of radon in domestic water supply will add about 1 pCi/l to the average indoor air concentration.

Bibliography
Benedict et al. 1981Manson Benedict, Thomas H, Pigford, and Hans Wolfgang Levi. Nuclear Chemical Engineering. New York: McGraw-Hill.
Eisenbud, Merril 1987Environmental Radioactivity From Natural, Industrial, and Military Sources. New York: Academic Press, Inc.
Myrick et al. 1983T.E. Myrick, B.A. Berven, and F. F. Haywood. Determination of Concentrations of Selected Radionuclides in Surface Soil in the U.S. Health Physics, Vol. 45, No. 5. Place: Pergamon Press.
NCRP 1984Exposures From the Uranium Series With Emphasis on Radon and its Daughters. Report No. 77. Bethesda, MD: National Council on Radiation Protection and Measurements (NCRP).
NCRP 1987Exposure of the Population in the United States and Canada from Natural Background Radiation. Report No. 94. Bethesda, MD: NCRP.
NCRP 1988Measurements of Radon and Radon Daughters in Air. Report No. 97. Bethesda, MD: NCRP.
UNSCEAR 1982United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Ionizing Radiation: Sources and Biological Effects. New York: United Nations Publication.
UNSCEAR 1993Sources and Effects of Ionizing Radiation. New York: United Nations Publication.
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Last updated: August, 1996