Radon, Part 2

1. Radon, Part 2 GLY 4241 - Lecture 11 Fall, 2014

2. Distribution of U and Th • Precursors of Rn • Distribution is quite uneven • Applies worldwide, although we will examine only the United States • Maps on following slides are from the United States Geological Survey

3. Uranium Distribution

4. Thorium Distribution

5. Living Area Radon • Median living-area radon concentrations pCi/L shown for each county in the United States

6. Home over 4 pCi/L

7. Eastern U.S. Sheared Rock Regions

8. Stanley Watras • Stanley Watras, an employee of the Limerick Nuclear Power Plant in Pottstown, PA, inadvertently discovered the danger in the Reading prong area by setting off radiation meters on numerous occasions • The problem got so bad that he was spending more time decontaminating than he was working • Mr. Watras finally had himself tested before entering the plant and he set off the monitors • His home was found to have a radon level more than 2000 pCi/L!

9. Granodiorite Deformation

10. Uranium Liberation • Granulation and fracturing play a minor role, especially with more resistant minerals such as uraniferous titanite and zircon • The grain-size reduction of these minerals may free uranium and make it available for chemical reaction and redistribution • Dynamic metamorphism releases fluids enriched in uranium, which migrate upward into the shear zone • Iron is released during metamorphism, and is often subsequently oxidized • Iron staining is commonly seen in the shear zones

11. U Redox • Iron oxidation allows reduction of uranium in the fluids, causing them to precipitate • Enrichment of uranium in the shear zone leads to increased radon emanation • The increased emanation is readily available to ground water in these permeable areas

12. Colebrookdale Township, West Side of Boyertown, Pa. • Radon measured in soil gas at 75 cm depth in the Boyertown, PA, area

13. Boyertown Indoor Radon • Indoor radon in Colebrookdale Township

14. Pennsylvania Radon Concentrations • Estimated median living-area radon concentrations

15. Radon: Land vs. Ocean • Radon gas emission is associated mainly with land areas • The oceans seem to be a sink for radon • The northern hemisphere contains a much higher percentage of land than the southern hemisphere • Thus, radon emissions are higher in the northern hemisphere • Atmospheric mixing between the northern and southern hemispheres is slow, so the average radon concentration in the northern hemisphere is higher than in the southern hemisphere • Total emissions form land are about 2.4 billion Ci/yr from continental land surfaces, versus about 23 million Ci/yr from the oceans

16. Drinking Water • Drinking or irrigation water drawn from areas where the ground water is in contact with radioactive elements is of concern • Radon is soluble in water and can reach appreciable concentrations • In 21 drilled wells in the Maine/New Hampshire region, Grune et al. (1960) found an average of 10,690 pCi/Liter of 222Rn • The maximum value was 176,000 pCi/Liter • They found an average of 65 and a maximum of 730 pCi/Liter of 226Ra from 224 wells or springs in Maine • In both Maine and New Hampshire, the water from drilled wells was more radioactive than water from dug wells

17. Radon Emanation Factors • U & Th presence necessary, but not sufficient • Other factors: • Host mineral type • Degree of Weathering • Layering in soils • Structural deformation – present? • Fracturing of host rock • Soil permeability • Soil moisture content • Atmospheric temperature and pressure variations

18. Permeability

19. Indoor Radon • Winter: Indoor radon problems are often far worse in winter, when buildings are tightly sealed, than in summer • Summer: In hot climates, where air-conditioned buildings may remain sealed for much of the summer, indoor radon problems likely to be worse in warm weather

20. Radon Precursor • The immediate parent isotope of radon is radium • It moves in soil mainly as the dipositive ion, Ra2+ • Ra is insoluble in the presence of moderate amounts of sulfate (SO42-) or carbonate (CO32-) • Ra generally coprecipitates with other substances, for example with barium in barite (Ba2+, Ra2+)SO4, or with calcium in calcite (Ca2+,Ra2+)CO3 • This may concentrate the parent isotope, but it does not inhibit radon release if the soil is otherwise permeable.

21. Marine Phosphorites • Marine phosphorites are shale deposits rich in the mineral apatite • Apatite is a calcium phosphate mineral • Anionic U groups readily substitute for phosphate • U is incorporated in the grain structure of the phosphate, and was deposited along with it • ∴ , uranium levels ∝ phosphorous levels • As a result, these rocks are usually strong emitters of radon • Other constituents of phosphates include vanadate, silicate, sulfate, and carbonate anions, and rare earth element and chromium cations

22. Fluor-apatite • Some phosphate rocks contain fluorine, as fluor-apatite • Fluorine ions may form soluble complexes with uranium, mobilizing it

23. Location of FL Phosphates • Florida has large deposits of phosphate ores • The phosphate deposits in Florida are primarily in Polk, Hillsborough, Manatee, and Hardee counties

24. Marine Phosphorites in Florida • Phosphate deposits in Florida consist of calcium fluorapatite (Ca10(PO4)6F2) in matrix • This matrix ranges from zero to 50 feet in thickness, averaging around 12 feet • The matrix is overlain by a leached zone that contains some aluminum phosphates, probably formed by the action of weathering and groundwater leaching on the upper part of the phosphate matrix

25. Indoor Rn Classification • The EPA has been the lead Federal agency studying the indoor Rn problem • They have formulated a series of levels, with recommended remediation actions for the higher levels • The Department of Housing and Urban Development (HUD) is also involved • HUD wants to insure that HUD-assisted housing will have low Rn levels (< 4 pCi/L) • HUD has been the lead agency studying 120,000 acres of reclaimed mined lands in Florida, and 300,000 additional acres of unmined lands with known phosphate deposits

26. Florida Radon Concentrations • Estimated median living-area radon concentrations

27. Radon Zones, Florida • Radon zones based on EPA data

28. Anthropogenic Spread of Radon • Man's activities have spread radioactive rock • U-bearing phosphate has been shipped to many areas, both inside and outside the United States, as fertilizer • Th-bearing granite has been used as grit in poultry farming • U mine tailings have been used as fill in urban developments • In other areas, tailings have washed or been dumped into rivers, where they can move downstream

29. Coal as a Reducing Agent • Coal acts as a reducing agent for any substance in contact with it • As a result it can reduce uranium from U6+ to U4+, which is generally insoluble • It precipitates into the coal matrix • With time the uranium decays to yield a variety of radioactive daughters • When the coal is mined, the radioactive daughters are also extracted • When the coal is burned, the radioactive elements are oxidized and emitted into the atmosphere • Much of the radioactivity is associated with the fly ash.

30. Coal Power • A major source of atmospheric radiation is the emission of various radioactive elements from coal-fired power plants • A large coal-fired plant without ash-control equipment can introduce several hundred millicuries of radionuclides into the atmosphere each year • This is much more than a nuclear power plant of the same power output would emit under proper operating conditions • An oil-burning plant would emit only about 0.1% as much radioactivity to the atmosphere

31. Fly Ash Disposal • In the United States about 1440 acres per year are used for fly-ash disposal • An alternative disposal method is to consolidate the fly-ash in blocks, but these blocks are then radon emitting for long periods • The United Kingdom dumps some fly-ash at sea • This has severe effects on marine life • Whether it introduces radioactive substance into the marine food chain is unknown • This could become a problem without an easy solution if radioactive element concentrations build up

32. U Mine Tailings • U mine tailings have been used as backfill, as soil conditioners, as a base for building foundations, and as concrete mix aggregate! • Rn from the tailings exudes from the ground through the foundation and walls of buildings, but is trapped inside the building • Mine tailings are often very fine particles that can be transported by the wind and deposited over wide areas

33. Grand Junction, Colorado • In the city of Grand Junction, Colorado, U mine tailings have been extensively used in construction, with the following results • Higher than normal radiation levels are common in buildings in Grand Junction • Incidence of cleft lip and palate is almost twice as great as the rest of Colorado • Birth rates are lower • The death rate from congenital deformities is 50% higher than the remainder of Colorado

34. Pomono, Colarado • The Pomona, Colorado Elementary School Annex provides another example • In summer, when the buildings are closed, the radiation levels reach eighteen times the level allowed in guidelines set by the Surgeon General of the United States

35. Uranium Distribution

36. Natural Sources of Radiation • Radon, 55%; • Cosmic sources and solar rays, 8%; • Terrestrial sources (mainly uranium and thorium), 8%; • Internal radiation (mainly 40K), 11%.

37. Anthropogenic Sources of Radiation • Medical x-ray, 11%; • Nuclear medicine, 4% • Consumer products (smoke detectors, tobacco, and ceramics), 3% • All others, 1%

38. Energy Efficiency • Energy efficiency has become an important environmental issue in recent decades • Many utility companies now pay homeowners, and sometimes businesses, to make their dwellings and industrial plants more energy efficient • One method of decreasing energy use is to seal the buildings as well as possible • If air does not enter or leave the building, less energy will be needed for heating or cooling • The effect of efficient building-seals is to decrease the flow of air into and out of windows, doors, and cracks • Attempting to seal the floor of the building is rare since little heat enters or leaves through the floor

39. Sealed Building Exposure • In a modern energy-conserving home the ventilation rate goes down to about one exchange per day • In the home in Boyertown cited earlier, the exposure would be about 250 rems per year, enough to cause radiation sickness and death within a few years • Many energy- efficient homes exceed the EPA limit of 500 millirems per year • In 1984, a federal judge in Utah awarded $2.6 damages to ten people as the result of atmospheric bomb tests in 1961-62 - their cumulative exposure was less than 500 millirems/year

40. Indoor Radon • Rn is chemically inert and ordinarily passes into and out of the lungs with no interaction • Rarely, it will decay while inside the lung, thus depositing solid radioactive daughter nuclides in lung tissues • Most Rn inside a structure will decay outside the lung • Since the radiation from Rn and its daughters is not very penetrating, it seems still to be a small concern

41. Radon on Dust and Smoke • Radon daughter nuclides are attracted and incorporated into dust particles • Dust particles may enter the lung and transport the solid radioactive particles with them, one reason that uranium miners have such high incidences of lung disease • Smoking, even passive smoking, is also very dangerous in high radon environments • The radioactive daughter nuclei readily stick to smoke particles, which penetrate into the lungs and stick much more readily than dust particles.

42. Anomalous Results • Around Cornwall, England radiation exposure averages more than a hundred times typical British exposures, with supposedly no increase in cancer • In Cumberland County, Pennsylvania the radon exposure is nine times higher than the U.S. average, but the lung cancer rate is well below U.S. average • In Finland the average radon levels are 2.5 pCi/Liter, or 2.5 times world average • Finnish women have a lung cancer rate of 70% of the average of other industrialized countries.

43. Conclusion • Attempts to alleviate the energy consumption increases sometimes have ramifications that were initially unexpected • One of these consequences is the exposure of the inhabitants of some dwellings too much higher than normal radiation levels, due to radon • Knowledge of geochemical distribution of radon precursors should serve as a warning before energy efficient structures are built • Anthropogenic activities, especially the improper disposal of uranium and/or thorium mine tailings, can greatly exacerbate this problem • Remedial action is extremely expensive and often does not restore the environment to an acceptable state