A 2-year study of seasonal indoor radon variations in northern Virginia.

Journal of Toxicology and Environmental Health

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A 2‐year study of seasonal indoor radon variations in Northern Virginia Douglas G. Mose , George W. Mushrush & Charles E. Chrosniak To cite this article: Douglas G. Mose , George W. Mushrush & Charles E. Chrosniak (1991) A 2‐year study of seasonal indoor radon variations in Northern Virginia, Journal of Toxicology and Environmental Health, 33:2, 115-130, DOI: 10.1080/15287399109531512 To link to this article: http://dx.doi.org/10.1080/15287399109531512

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A 2-YEAR STUDY OF SEASONAL INDOOR RADON VARIATIONS IN NORTHERN VIRGINIA Douglas G. Mose, George W. Mushrush, Charles E. Chrosniak

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Center of Basic and Applied Science, George Mason University, Fairfax, Virginia

The concentrations of indoor radon in the basements of homes located in northern Virginia average about 1.4 times the first-floor radon concentrations. Basement indoor radon concentrations exhibit seasonal variations that can be related to home use patterns of the occupants. Little indoor radon difference was seen between homes that have concrete block basement walls and poured concrete basement walls, but homes that use oil or gas furnaces for heating have ~25% lower indoor radon than homes that use electrical heating systems. Particular geological units seem to be associated with elevated indoor radon concentrations, and several units are associated with indoor radon concentrations that exceed 4 pCi/l (the U.S. Environmental Agency "action level") at some time in more than 40% of the homes. Comparative studies between indoor radon and total gamma aeroradioactivity show that aeroradioactivity can be accurately used to estimate community radon hazards. When combined with information about the home heating system, geology and aeroradioactivity can be used to identify problem homes.

INTRODUCTION The magnitude of natural radioactivity from radon was not realized until 1984 when discovery of excessively high levels of radon gas in a home in Boyertown, Pa., aroused national concern (Lafavore, 1986). Because of health implications, the early work on indoor radon has given rise to a broad range of research characterizing 222Rn and progeny occurrence and control in inhabited structures (Alter and Oswald, 1987; Nero, 1988). With the tendency for the gas to concentrate in buildings where air exchange is limited, radon is becoming identified as a major form of indoor air pollution. There is growing belief that exposure to radon gas poses one of the nation's most significant radiological health problems in the form of an increased risk of developing lung cancer (National Research Council Committee on the Biological Effects of Ionizing Radiation, 1988). The consequences of exposure to radon and its daughters in high concentrations is well documented in the literature from studies of uranium miners (NIOSH, 1985). Studies have shown that inhalation of 222Rn Requests for reprints should be sent to Douglas G. Mose, Department of Geology, George Mason University, Fairfax, VA 22030. 115 Journal of Toxicology and Environmental Health, 33:115-130, 1991 Copyright © 1991 by Hemisphere Publishing Corporation


116

D. G. MOSE ET AL.

and its progeny can result in radiation doses that exceed all other doses from natural radiation sources (Puskin and Yang, 1988). This concern has intensified since the discovery that inhaled radon passes through the lungs to be dissolved in body fluids and tissues (Pohl and Pohl-Ruling, 1967; Lykken and Ong, 1989; Henshaw et al., 1990; Gosink et al., 1990), and consequently may initiate soft-tissue cancers. The effect of alpha radiation from the inhalation of radon daughters is somatic rather than genetic in nature. The problem arises because the very short half-lives of radon and its daughters allow the disintegrations to occur on the epithelial lining of the lungs before the mucociliary clearance system has a chance to move the particles out of the lungs. The body has repair mechanisms that can handle damage from radiation. However, if the rate at which the cells are damaged or destroyed is greater than the body's ability to repair them, the damage will be cumulative. The National Research Council Committee on the Biological Effects of Ionizing Radiation recently estimated the risk of radon exposure that supports EPA's earlier calculation of 5000 to 20,000 deaths per year (National Research Council Committee on the Biological Effects of Ionizing Radiation, 1988). Uranium in soil and rock is the source of most radon to which people are exposed. The importance of soil as a source of indoor radon combined with the increasing evidence of unacceptably high radon concentrations in a significant fraction of houses has raised the question of whether one might predict on a geological basis where high indoor radon levels might be found. The potential for high indoor radon concentrations depends on several factors: radium content of the soil, moisture content of the soil, permeability of the soil, the season, and the weather. Radon gas enters the atmosphere by crossing the soil-air interface. It is estimated that the emanation rate is 0.42 pCi/m2/s from soil in the United States (National Council on Radiation Protection and Measurements, 1984). The observed indoor concentration of radon and its progeny depends on three factors: the entry or production rate from the source, the ventilation rate, and the rate of removal. Because of radium's long halflife and lack of chemical reactivity, 222Rn itself acts much like a stable pollutant whose concentration can be determined by a comparison of the entry and ventilation rates. The decay products are somewhat more complex, but as a practical matter the decay product concentration is indicated approximately by the overall radon concentration. To determine if elevated radon concentrations are a problem in the central Appalachians, the Center of Basic and Applied Science at George Mason University is conducting an in-depth regional survey in Virginia. This paper reports on results for eight consecutive 3-mo intervals using alpha-track detectors. It will be shown that the observed indoor radon concentrations are related to the season, the floor on which the mea-

2 YEARS OF RADON IN VIRGINIA

117

sûrement is taken in the home, the type of home heating system, the geological material under the home, and aerial radiation data.


METHOD The indoor radon situation as it existed in the three geological provinces that comprise the terrane of Fairfax County in northern Virginia (Fig. 1) is described in this paper. The three Appalachian provinces that comprise the terrane of northern Virginia (Froelich, 1985) are the Coastal Plain, the Piedmont, and the Culpeper Basin. They are depicted in Figures 1 and 2. The Coastal Plain Province is located along the eastern edge of the study area. It consists of poorly cemented clastic sedimentary strata, mostly layers of clay and sand, that were deposited during the opening of the modern Atlantic Ocean. These deposits were formed between about 130 million years ago and the present. The Piedmont Province extends from Maine to Georgia, and rock units of this province underlie most of the central part of the northern Virginia study area. The Piedmont geologic units are composed of metamorphic and igneous rocks that were formed when the Appalachian Mountains were created during the Paleozoic Era, about 600-300 million years ago. The western margin of the study area is part of the Culpeper basin, a fault-bounded valley containing terrestrial clastic rocks (siltstone, sandstone, conglomerate) along with extrusive and intrusive igneous rocks (diabase) that were all deposited during the Mesozoic Era, about 190-150 million years ago. The indoor radon values were obtained from November of 1986 through October of 1988, using seasonal measurements during winter periods (November-January), spring periods (February-April), summer periods (May-July), and fall periods (August-October). The number of participants accounts for about 0.5% of the total homes in Fairfax County. The test program required that each of the homeowners participate in a four-season testing period. The homeowner provided an exact location on a county map, which made it possible to identify the geologic rock unit underlying the home and to locate the home on a totalgamma aerial radiation map. The homeowners filled out a questionnaire that provided information on home construction, basement wall construction, the type of heating system, and many other factors. Specific instructions were given for the monitor placement. The conclusions are based on 3-mo indoor radon measurements using alpha-track radon monitors provided by Tech/Ops Landauer Corporation of Illinois. After the exposure period, the monitors are returned to Tech/Ops for analysis. Tech/Ops develops the film in the monitors, measures the "tracks" produced by the decay of radon progeny near the film surface, and calculates the average amount of indoor radon recorded by


CO

CED Coastal Plain • Piedmont Province • Culpeper Basin 10 km 5 miles FIGURE 1. Generalized geological map of Fairfax County, Va.

119



10 km

FIGURE 2. Detailed geological map of Fairfax County, showing the location of geological units. Index to map: 1, Coastal Plain sedimentary strata; 2, Piney Branch Complex (mafic and ultramafic rocks); 3, unnamed mafic and ultramafic inclusions; 4, Occoquan Granite; 5, Falls Church Tonalité; 6, Sykesville Formation (metasedimentary melange); 7, Indian Run Formation (metasedimentary melange); 8, Annandale Group (mica schist and graywacke); 9, Popes Head Formation (phyllite and siltstone); 10, Peters Creek Schist (mica schist, metagraywacke and phyllite); 11, Culpeper Basin diabase intrusions and basaltic extrusions; 12, Culpeper Basin sedimentary rocks.

the film. The humidity and temperature insensitivity and permanent record keeping are probably the major advantages of alpha-track monitors. These inexpensive alpha-track monitors with their small fragment of film require at least 1 mo for enough tracks to accumulate in a typical home to generate a useful measurement. Estimates of uncertainty for the alpha-track monitors are related to the measurement interval, so intervals of 3 mo were used in this study. At the 90% confidence level, the alpha-track monitors carry an uncertainty of about ±25% for the 3-mo measurement interval, and a ±50% uncertainty if used to estimate the average year-long radon concentration (Mose et al., 1990). RESULTS AND DISCUSSION Table 1 is a summary of the measurements obtained over the eight seasons of study in northern Virginia homes. Most of the homeowners

120

D. C. MOSE ET AL.

TABLE 1. Summary of Basement and First-Floor Indoor Radon over Eight Seasons

Measurement season

Average radon (pCi/l)

Median radon (pCi/l)

% Over 4 pCi/l

% Over 10 pCi/l

Number of homes


Basement Winter 11/86-1/87 Spring 2/87-4/87 Summer 5/87-7/87 Fall 8/87-11/87

5.1 4.2 3.0 3.8

3.9 2.9 2.4 3.0

49% 33% 23% 34%

9% 6% 2% 3%

286 487 735 772

Winter 11/87-1/88 Spring 2/88-4/88 Summer 5/88-7/88 Fall 8/88-10/88

4.0 3.9 4.2 6.2

2.8 3.0 3.5 4.2

33% 33% 41% 53%

5%

525 334 126 108

Winter 11/86-1/87 2/87-4/87 Spring Summer 5/87-7/87 Fall 8/87-11/87

3.4 2.6 2.1 2.7

2.4 1.6

23% 16% 11% 21%

5%

Winter 11/86-1/87 Spring 2/87-4/87 Summer 5/87-7/87 Fall 8/87-11/87

2.9 3.1 3.0 4.5

2.1 2.0 1.8 3.9

23%

2%

24% 32% 50%

2% 0% 5%

5%

5% 9%

First Floor

1.6 2.2

4% 0% 0%

39 76 125 115 100 59 22 20

placed their radon monitors in a basement location (approximately 90% of the study homes have a basement). During most seasons, radon on the first floor above the ground contained radon at about 70% of the basement concentration. Similar observations about the basement versus first floor difference has recently been noted by others in the United States (e.g., Perritt et al., 1990) and elsewhere (e.g., Buchli and Burkart, 1989; Crameri et al., 1989). Also, the pattern of seasonal variations has been observed in many parts of the United States (e.g., Cohen and Gromicko, 1988; Dudney and Hawthorne, 1990; Steck, 1990). Table 2 shows that homes equipped with an oil or gas heating system tend to have lower levels of indoor radon than homes equipped with an electrical heating system. It seems reasonable that the difference relates to the influx of essentially radon-free air from outside the home. During the winter and during heating days in the spring and fall, homes heated with a combustion system experience a brief low-pressure interval when the furnace ignites, driving air out of the basement in the form of chimney gasses. The momentary low-pressure interval is immediately eliminated as outside radon-free air is drawn into the home, around windows and doors. The indoor radon levels of homes with oil or gas heating systems are also lower in the summer than in homes with electrical heat-



121

¡ng systems. This unexpected result is probably because of the wholehome air cooling ability of the heat pump, which is the most commonly used electrical heating system in the study area. During the summer, homes with the whole-home service of heat pumps are often closed to keep the warm but also radon-free outside air from entering the home. Table 3 shows that during about half of the seasonal intervals, homes with concrete block basement walls have higher indoor radon, compared to homes with basements with poured concrete walls, but the situation is reversed during the other seasons. Although walls composed of concrete blocks commonly accumulate cracks in the mortar, and the blocks can be quite permeable, both of which facilitate the entry of radon from the surrounding soil, the effect must be small and is apparently masked by other factors. Table 4 shows the seasonal indoor radon associated with the geological units in Fairfax County (Fig. 3). Measurements grouped in this fashion show that some rock units are seasonally and on average associated with twice as much indoor radon compared to other units. The difference between the Coastal Plain and the Piedmont is similar to that noted by Watson et al. (1988) in North Carolina. In both North Carolina and Virginia, the Coastal Plain has a lower indoor radon level than the Piedmont. TABLE 2. Summary of Basement Indoor Radon from Homes That Use Oil and Gas Heating, and from Homes That Use Electrical Heating Measurement season

Heating system

Average (pCi/l)

Median (pCi/l)

% Over 4 pCi/l

Winter

11/86-1/87

Spring

2/87-4/87

Summer

5/87-7/87

Fall

8/87-10/87

Oil/gas Electrical Oil/gas Electrical Oil/gas Electrical Oil/gas Electrical

5.0 5.6 4.0 4.5 2.7 3.7 3.5 4.6

3.8 4.1 2.9 3.0 2.3 2.8 2.9 3.5

46% 50% 34% 37% 18% 31% 30% 44%

130 102 234 154 381 215 407 224

Oil/gas Electrical Oil/gas Electrical Oil/gas Electrical Oil/gas Electrical

3.6 5.0 3.4 4.8 3.1 5.0 4.8 8.1

2.6 3.4 2.7 3.5 2.5 3.9 3.7 4.5

29% 42% 27% 44% 32% 48% 44% 61%

291 143 186 107 59 61 61 44

Oil/gas Electrical

3.5 4.9

2.7 3.4

29% 42%

1800 1085

Winter

11/87-1/88

Spring

2/88-4/88

Summer

5/87-7/88

Fall

8/88-10/88

Eight-season summary

Number of homes

122

D. G. MOSE ET AL.

TABLE 3. Summary of Basement Indoor Radon from Homes That Have Concrete Block Basement Walls and from Homes That Have Poured Concrete Basement Walls


Measurement season Winter

11/86-1/87

Spring

2/87-4/87

Summer

5/87-7/87

Fall

8/87-10/87

Winter

11/87-1/88

Spring

2/88-4/88

Summer

5/88-7/88

Fall

8/88-10/88

Eight-season summary

Type of basement wall

Average (pCi/l)

Median (pCi/l)

% Over 4 pCi/l

Block Poured Block Poured Block Poured Block Poured

5.5 4.3 4.4 3.7 3.0 3.0 3.8 3.9

4.1 3.4 3.0 2.7 2.5 2.3 3.0 3.2

52% 40% 36% 26% 24% 19% 34% 34%

183 92 310 156 469 237 483 244

Block Poured Block Poured Block Poured Block Poured

3.8 4.1 3.7 4.3 3.8 4.6 4.9 8.9

2.7 2.8 2.8 3.1 3.4 3.5 4.0

31% 34% 30% 38%

335 160

Block Poured

4.1

3.9

Number of homes

41%

216 112 81

4.5

40% 51% 55%

40 73 31

2.9 2.9

34% 32%

2219 1100

Because of the great density of measurements in the northern Virginia study area (over 3000 basement measurements and over 500 firstfloor measurements in an area of about 1000 km2), it is possible to detect differences between geological units. As in North Carolina, the area of lowest indoor radon (—2.0 pCi/l) is found to be the undivided Coastal Plain, but almost as low averages (less than 2.5 pCi/l) occur over the intrusive rocks in the Piedmont and the Culpeper Basin. The areas of highest indoor radon (more than 3.5 pCi/l) occur over the Peters Creek Schist in the Piedmont and over the siltstone and shale unit in the Culpeper Basin. These observations are of concern, as these units underlie an area currently used for construction of the suburban community being developed west of Washington, D.C. It is interesting to note that in the Piedmont Province, the phyllite and schist rock units (e.g., Annandale Group, Popes Head Formation, Peters Creek Schist) and not the granitic rocks showed the highest values of indoor radon. Several studies have commented upon granite as a rock normally associated with above-average radon levels (Alter and Oswald, 1987; Nero, 1988). This apparent contradiction concerning the indoor radon potential for granitic rocks is resolved by understanding the effect of recrystallization on granite. In general, uranium is often enriched in granite rock when it is first emplaced and crystallized. Homes over a soil


123


TABLE 4. Summary of Basement Indoor Radon from Homes Constructed Over the Geological Units That Underlie Fairfax County

Geological rock unit

Measurement season



% Over 4 pCi/l

Coastal Plain: Sedimentary Strata

Winter 86/87 Spring 1987 Summer 1987 Fall 1987 Winter 87/88 Spring 1988 Summer 1988 Fall 1988

3.3 2.5 1.9 2.4 2.6 2.3 2.4 3.2

2.6 2.0 1.7 2.1 2.0 1.9 2.0 2.7

21% 14% 7% 8% 16% 14% 13% 14%

28 49 92 97 70 44 8 6

2-yr Average

2.4

2.0

12%

394


3.9 3.3 2.2 2.4 1.9 2.1 2.9 2.9

4.4 2.7 1.4 1.7 1.9 1.9 2.9 2.9

80% 38% 25% 20% 0% 0% 0% 0%

5 8 12 10 6 4 1 1

2-yr Average

2.6

2.2

26%

47


3.3 3.0 2.6 3.0 3.0 3.5 4.0 6.9

3.1 2.2 2.0 2.5 2.2 3.0 1.7 4.8

20% 17% 13% 18% 19% 33% 33% 50%

15 30 54 56 42 24 6 8

2-yr Average

3.1

2.4

20%

235


3.5 2.8 2.2 3.0 2.7 2.4 2.1 7.0

3.2 2.0 2.3 2.2 2.2 2.2 2.5 2.7

22% 25% 10% 18% 20% 0% 0% 33%

9 16 21 22 10 9 3 3

2-yr Average

2.8

2.3

16%

93

Piedmont: Piney Branch Mafic and Ultramafic Complex and Unnamed Mafic and Ultramafic Inclusions

Piedmont: Occuquan Granite

Piedmont: Falls Church Tonalité

Number of homes

{Continued on next page)

124

D. G. MOSE ET AL.


TABLE 4. Summary of Basement Indoor Radon from Homes Constructed Over the Geological Units That Underlie Fairfax County (Continued)


Measurement season



% Over 4 pCi/l

Number of homes

Piedmont: Sykesville Formation (metasedimentary melange)


5.0 3.7 2.9 4.2 3.9 3.6 3.0 5.0

3.8 2.8 2.4 3.1 2.6 2.3 2.1 4.0

44% 29% 20% 29% 22% 20% 22% 44%

41 59 107 118 76 46 9 9

2-yr Average

3.8

2.8

26%

465


3.7 2.8 2.6 3.0 2.7 2.4 4.5 5.6

3.4 2.5 1.8 2.6 2.3 1.9 4.0 6.4

50% 17% 14% 20% 18% 21% 67% 50%

14 24 36 40 28 14 6 6

2-yr Average

2.9

2.6

23%

168


3.6 4.1 3.2 4.0 5.0 4.4 4.7 5.3

3.3 2.9 2.6 3.5 4.3 4.0 4.4 4.8

37% 27% 31% 40% 53% 50% 64% 65%

19 33 52 57 40 28 11 8

2-yr Average

4.1

3.5

41%

248


6.6 4.7 3.5 4.0 4.2 3.8 3.7 4.9

5.3 3.2 2.8 3.3 2.6 2.7 3.5 4.5

67% 40% 24% 39% 29% 28% 41% 52%

24 53 86 84 62 43 17 21

2-yr Average

4.2

3.2

36%

390

Piedmont: Indian Run Formation (metasedimentary melange)

Piedmont: Annandale Group (mica schist and metagraywacke)

Piedmont: Popes Head Formation (phyllite and metasiltstone)


125


TABLE 4. Summary of Basement Indoor Radon from Homes Constructed Over the Geological Units That Underlie Fairfax County (Continued)


Measurement season

Piedmont: Peters Creek Schist (mica schist, metagraywacke and phyllite)

Winter 86/87 Spring 1987 Summer 1987 Fall 1987 Winter 87/88 Spring 1988 Summer 1988 Fall 1988 2-yr Average

Culpeper Basin: Diabase Intrusions and Basaltic Extrusions

Culpeper Basin: Siltstone and Shale

Culpeper Basin: Conglomerate and Sandstone



% Over 4 pCi/l

Number of homes

6.5 5.5 3.8 4.9 5.0 5.1 5.0 7.8

4.8 3.6 3.3 4.1 4.0 3.8 3.9 3.8

61% 47% 36% 53% 52% 48% 45% 41%

97 155 193 202 135 79 42 27

5.1

3.9

48%

930

3.2 1.9 1.7 2.3 2.2 2.6 2.2 . 4.3

38% 21% 0% 14% 20% 33% 25% 50%

8 14 22 22 15 12 4 4


3.8 2.7 1.9 2.7 3.9 6.2 4.8 12.8

2-yr Average

3.7

2.3

19%

101


7.4 7.2 5.4 5.8 4.8 4.6 3.5 5.2

4.7 9.6 2.7 4.2 4.6 5.5 2.6 4.0

67% 60% 38% 44% 57% 80% 25% 67%

3 5 8 9 7 5 4 3

2-yr Average

5.5

4.6

52%

44


4.0 3.4 2.6 3.2 3.4 3.2 5.5 7.5

3.0 2.6 1.9 2.5 2.0 3.0 6.5 6.2

37% 19% 13% 26% 20% 67% 67% 67%

19 37 40 39 20 6 3 3

2-yr Average

3.3

2.5

25%

167

'

D. G. MOSE ET AL.

126

AERORADIOACTIVITY

•

Highest

E3 Intermediate im Lowest


No Data

FIGURE 3. Map showing areas of different aeroradioactivity (and different potential for indoor radon problems) in Fairfax County (modified from Daniels, 1980). Index to map: Highest, over 400 counts per second; Intermediate, 200-400 counts per second; Lowest, less than 200 counts per second; No Data, areas where abrupt changes in aeroradioactivity signals appear to be due to problems related to equipment calibration.

derived from such granites, commonly found in portions of most major mountain systems, would tend to have elevated indoor radon. In the Fairfax County study area, most of the granitic rocks were recrystallized during postemplacement deformation associated with mountain building. The recrystallization process tends to displace uranium to the surface of minerals as they reform during such rock deformation. The uranium is thus easily removed by the passage of intergranular water. Uranium is consequently displaced into the host rock of the granite, such as the gneiss, or into more distant rock units such as the phyllite or schist. In addition to the home heating system and geology, surface radiation was studied as a key to locating problem communities. Surface radiation is currently of some interest as a tool for locating problem areas on a national scale (Revzan et al., 1988). The radiation signal of the earth's surface in the northern Virginia study area is rather better known than perhaps anywhere else in Virginia (Fig. 3). Total-count gamma-ray radioactivity measurements were flown with a ground clearance about 500 ft along east-west flight lines. The flight lines were spaced at only Vi mi apart over Fairfax County (Daniels, 1980). At this altitude the effective area of response of the scintillation equipment is approximately 1000 ft in diameter, and the signal is generated by the uppermost 1 ft into the ground. The combination of close flight lines and area of response is such that essentially all of the ground surface was examined for its radioactivity signal. This type of survey is potentially very useful, though there are some disadvantages. One problem is that the total surface is examined, including manmade structures (pavements, buildings, etc.) and water. However, these comprise only a small percentage of the total land surface. Another



127

problem, at least for radon surveys, is that the data are total gamma-ray radioactivity, derived from 214Bi (a radioactive daughter of uranium, produced by the decay of a2Rn), thorium, and potassium. However, to a rough approximation uranium, thorium, and potassium tend to have a similar geochemical behavior. Potassium-rich rocks tend to be enriched in uranium and thorium. Furthermore, as will be shown below, there is a good correlation between indoor radon and the total gamma-ray signal, suggesting that the component of the total signal due to 222Rn is relatively constant percentage of the total signal. The aeroradioactivity map for Fairfax County was examined to evaluate its use as a predictor of indoor radon. The comparison between indoor radon levels, measured in terms of the percentage of homes over 4 pCi/l during the winter, and aeroradioactivity is rather good (Table 5; a similar comparison occurs for the other three seasons). For most of the comparisons between aeroradioactivity and basement-level indoor radon measurements, indoor radon increases as the aeroradioactivity increases. Among the 23 radon versus aeroradioactivity comparisons in Table 5, there are 2 cases of anomalously low indoor radon and 2 cases of anomalously high indoor radon. The reason for this variance is not known, but it may be that in these cases, local variations in aeroradioactivity not shown on the aerial survey are responsible. Although interesting, the greater significance arises from the observation that in general, regional aeroradioactivity is closely tied to indoor radon in homes constructed over a variety of geological units. Perhaps the most significant advantage of the Fairfax County aeroradioactivity survey is that the survey covers essentially all of the county surface. This makes such surveys a cost-effective improvement over an analogous land-based study in which a geologist would examine the radon emanation characteristics of all the area underlain by each geological unit. A comparable land-based study based mainly on geological units and soil types would probably be always less useful because, as can be demonstrated by comparing geological maps with aeroradioactivity maps for the study area, most rock units vary in surface radioactivity. Another advantage of aeroradioactivity surveys is that the "uranium signal" is actually the gamma-ray emission of 214Bi, a daughter product of 222 Rn. In other words, the total gamma-ray signal is directly related to radon. This effectively eliminates concern for the observation that variable amounts of uranium are lost by weathering (Daniels, 1980). CONCLUSIONS Indoor radon and its progeny are a serious problem in northern Virginia and elsewhere. In the present study, the indoor radon concentrations can be related to the floor of home measurement, the season, the

128

D. G. MOSE ET AL.


TABLE 5. Comparison of Total Gamma Aeroradioactivity to Basement Level Indoor Radon Measurements

Fairfax County geological unit



Coastal Plain Sedimentary Strata Aeroradioactivity - 100-200 cps Aeroradioactivity - 200-300 cps

2.9 2.3

2.3 2.3

18% 10%

17 10

Piedmont Occoquan Granite Aeroradioactivity — 100-200 cps Aeroradioactivity - 200-300 cps

2.1 3.4

2.3 2.2

0% 24%

12 21

Piedmont Sykesville Formation Aeroradioactivity - 100-200 cps Aeroradioactivity - 200-300 cps Aeroradioactivity - 300-400 cps

2.2 4.7 5.2

2.6 2.7 4.1

0% 27% 38%

8 15 53

Piedmont Indian Run Aeroradioactivity = Aeroradioactivity = Aeroradioactivity -

Formation 100-200 cps 200-300 cps 300-400 cps

2.7 3.2 3.5

2.2 3.3 3.9

14% 31% 57%

7 29 7

Annandale Group Aeroradioactivity - 200-300 cps Aeroradioactivity - 300-400 cps

4.7 4.8

3.2 4.4

36% 58%

22 31

Popes Head Formation Aeroradioactivity - 100-200 Aeroradioactivity = 200-300 Aeroradioactivity - 300-400 Aeroradioactivity = 400-500

cps cps cps cps

5.3 3.6 4.8 8.4

4.9 2.7 3.2 5.1

62% 21% 40% 67%

8 14 63 6

Peters Creek Schist Aeroradioactivity = Aeroradioactivity Aeroradioactivity = Aeroradioactivity -

cps cps cps cps

4.8 4.7 7.8 9.1

4.0 4.0 5.0 8.1

53% 50% 62% 100%

17 113 85 4

and Sandstone cps cps cps

2.4 4.7 3.5

2.0 3.0 2.1

9% 44% 33%

11 23 6

200-300 300-400 400-500 500-600

Culpeper Basin Conglomerate Aeroradioactivity - 200-300 Aeroradioactivity = 300-400 Aeroradioactivity - 400-500

% Over 4 pCi/l

Basement data

Note. Percentages of homes over 4 pCi/l represent estimates where at least 4 homes were measured for indoor radon (* — cases where indoor radon is anomalously low; ** — cases where indoor radon is anomalously high).

type of home heating system, the geology, and the aerial radiation survey of a region. Basement measurements usually exceed first-floor measurements, and winter measurements were usually the highest. Spring and fall indoor radon values were comparable, and the summer season tends to be the time of lowest values. Homes with electrical heating systems tend to have higher indoor radon than homes with oil or gas furnaces.


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Homes constructed on particular geological units in the Piedmont tend to have the highest radon measurements, as do homes constructed in areas with higher total-gamma surface radiation. It is obvious that with some care a potential homebuyer can select a home with factors that can be associated with a low indoor radon concentration. It is also clear that owners of presently occupied homes can be alerted to a potential indoor radon problem if they are informed about factors that contribute to a radon hazard. REFERENCES Alter, H. W., and Oswald, R. A. 1987. Nationwide distribution of indoor radon measurements, a preliminary data base. J. Air Pollut. Control Assoc. 37:227-231. Buchli, R., and Burkart, W. 1989. Influence of subsoil geology and construction technique on indoor air 222-Rn levels in 80 houses of the central Swiss Alps. Health Phys. 56:423-429. Cohen, B. L., and Gromicko, N. 1988. Variations of radon levels in U.S. homes with various factors. J. Air Pollut. Control Assoc. 38:129-134. Crameri, R., Brunner, H., Buchli, R., Wernli, C., and Burkart, W. 1989. Indoor Rn levels in different geological areas in Switzerland. Health Phys. 57:29-38. Daniels, D. L. 1980. Geophysical-geological analysis of Fairfax County, Virginia. U.S. Geol. Survey Rep. 80-1165. Dudney, C., and Hawthorne, A. 1990. Radon-222, Rn-222 progeny, and Rn-220 progeny levels in 70 houses. Health Phys. 58:297-311. Froelich, A. J. 1985. Folio of geologic and hydrologic maps for land use planning in the coastal plain of Fairfax County and vicinity, Virginia. U.S. Geol. Survey Misc. Invest. Ser., map 1-1423. Gosink, T. A., Baskaran, M., and Holleman, D. F. 1990. Radon in the human body from drinking water. Health Phys. 59:919-924. Henshaw, D. L., Eatough, J. P., and Richardson, R. B. 1990. Radon as a causative factor in induction of myeloid leukaemia and other cancers. Lancet 335:1008-1012. Lafavore, M. 1986. Radon, The Invisible Threat. Emmaus, Pa.: Rodale Press. Lykken, G. I., and Ong, W. S. 1989. Evidence of exhalation of stored environmental Rn determined by whole-body counting. Health Phys. 57:61-162. Mose, D. G., Mushrush, G. W., and Chrosniak, C. E. 1990. Reliability of inexpensive charcoal and alpha-track radon monitors. Natural Hazards 3:341-355. National Council on Radiation Protection and Measurements. 1984. Exposures from the Uranium Series with Emphasis on Radon and Its Daughters. Report no. 77. National Institute for Occupational Safety and Health. 1985. Evaluation of Epidemiologic Studies Examining the Lung Cancer Mortality of Underground Miners. Cincinnati: NIOSH. National Research Council Committee on the Biological Effects of Ionizing Radiation. 1988. Health Risks of Radon and Other Internally Deposited Alpha-Emitters. Washington, D.C.: National Academy Press. Nero, A. V. 1988. An overview. In Radon and Its Decay Products in Indoor Air, eds. A. Nero and W. Nazaroff, pp. 1-47. New York: Wiley. Perritt, R., Hartwell, T., Sheldon, L., Cox, B., Clayton, C., Jones, S., and Smith, M. 1990. Radon-222 levels in New York State homes. Health Phys. 58:147-155. Pohl, E., and Pohl-Ruling, J. 1967. The radiation dose received by inhalation of air containing Rn222, Rn220, Pb212 (ThB) and their decay products. Ann. Acad. Brasil. Ciencias 39:393-404. Puskin, J. S., and Yang, Y. 1988. A retrospective look at Rn-induced lung cancer mortality from the viewpoint of a relative risk model. Health Phys. 54:635-643. Revzan, K., Nero, A., and Sextro, R. 1988. Mapping surficial radium content as a partial indicator of radon concentrations in US houses. Radiat. Protection Dosimetry 24:179-184.

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Steck, D. 1990. A comparison of EPA screening measurements and annual Rn-222 concentrations in statewide surveys. Health Phys. 58:523-530. Watson, J. E., Jr., Adams, W., and Xie, Y. 1988. Survey of Rn-222 in North Carolina homes. Health Phys. 55:71-75.


Received October 5, 1990 Accepted January 25, 1991

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