The Science of the Total Environment, 121 (1992) 53-66 Elsevier Science Publishers B.V., Amsterdam

53

Radon concentrations inside castles and other ancient buildings Alberto Malanca a, Rosella Orlandini b, Valerio Pessina c and Giuseppe Dallara c aDipartimento di Fisica, Universita' di Parma, Viale delle Scienze, 43100 Parma, Italy bAssessorato all'Ambiente, 42100 Reggio Emilia, Italy cPMP, Setwre Fisico Ambientale USL no. 4, Via Spalato, 4, 43100 Parma, Italy (Received May 10th, 1991; accepted August 5th, 1991)

ABSTRACT Sixty-two measurements of Rn-222 concentrations were made in 24 castles and 13 ancient buildings in 30 different places situated in the provinces of Parma and Reggio Emilia (Northem Italy). The method used was that of activated carbon canisters which were placed in selected settings for at least 48 h in the period starting from December 1990 to May 1991. It was possible to determine the amount of radon in each canister via its daughters gamma emitters counted by NaI(TI) and Ge(I) detectors. The mean radon concentrations were 72 Bq m -3 (arithmetic mean) and 49 Bq m -3 (geometric mean), a good deal higher than the values obtained from measurements carried out in modem dwellings in the same area; 30 Bq m -3 (arithmetic mean) and 19 Bq m -3 (geometric mean).

Key words: radon-222; charcoal canister method; castles; buildings; bricks

INTRODUCTION

Radon-222 (radon), is a noble radioactive gas generated by the disintegration of Ra-226 which is present in soil, water and building materials. Various attempts have been made to correlate the radon concentration in dwellings with one or more of the following variables: surface radium contents in soils and soil permeabilities (Nazaroff et al., 1985); distribution of external gamma dose rate and uranium in bedrock and soils (Castren et al., 1985); building materials and construction characteristics (Wolfs et al., 1984); height of the building (Gesell, 1983) and ventilation rate (Nero et al., 1983). More recently a few authors have taken into consideration the age of the building as a variable to be considered when dealing with radon levels in a set of dwellings. George and Hinchliffe (1987), determined radon concentra0048-9697/92/$05.00

© 1992 Elsevier Science Publishers B.V. All rights reserved

54

A. MALANCA ET AL.

tions in 380 buildings in the eastern United States and found no correlation between the age of the houses and radon levels. Stranden (1987), on the basis of measurements in 1500 dwellings in Norway, plotted the mean radon concentration against the age of the house without finding any systematic variations between the two variables. Cohen (1987) reports little correlation between radon and age in homes in Pennsylvania and New Jersey. Swedjemark (1980) noted an increase of the radiation dose in Swedish houses built after 1950 probably due to a decrease of air exchange rates. However, in the studies cited only buildings < 100 years of age were considered. In many countries such as the United States or Scandinavia, most people live in single detached new houses. In Italy a small, but significant number of people still live in houses which may be very old, up to 1000 years. The aim of the present research is to establish a possible correlation between radon concentration and the age of the buildings. To accomplish that we could not choose old houses in town since, generally, householders do not know when they were built; moreover, nearly all of the residential buildings have suffered substantial transformations in the last decades in order to fulfil the needs of modem life; partition walls, new floors, plaster, tiles, wallpaper, doors and double-glazed windows have been added. Fortunately, owing to the relatively large number of historical buildings in Italy, we could select 24 castles and 13 ancient buildings in 30 different places situated in the provinces (administrative units) of Parma and Reggio Emilia. Most of them were inhabited or used as workplaces. MATERIALS AND METHODS The charcoal canister method (Cohen and Cohen, 1983) has been used for sampling radon gas in 62 rooms in castles and other ancient buildings in the period starting from December 1990 to May 1991. Figure 1 shows the locations monitored. The canisters were exposed in ground and upper floors after obtaining permission from owners or responsible authorities, for at least 48 h to provide integrated environmental levels of radon. None of the rooms surveyed had air conditioning or forced ventilation. No canisters were placed in attics, basements, cellars or other settings where people are hardly likely to live. The windows were generally old, in only one case was there double glazing. Rooms with frescoes were selected whenever possible to make sure that they had not been recently plastered. Each canister, consisting of a cylindrical metallic can, contained 70 g of activated carbon. The gamma emission due to K-40 in the charcoal was < 3.7 × 10 -2 Bq. Owing to the short half-lives of the radon daughters, compared to that of radon itself, the equilibrium between Rn-222, Pb-214 and Bi-214 is rapidly attained in the canister. The amount of radioactivity adsorbed in

55

RADON CONCENTRATIONS IN ANCIENT BUILDINGS

I

T

A

L

Y

11 7

25

14

9

26

8

PARMA 2

15

12

J¢

1 6 ~

REGGIO 24 E M I L I A

21

13 18

2"~'~ ,

27 "~

30

"'"~-~ 28 10

23

29

"~

J

20

0 I

I km

10 I

Fig. 1. Map of the provincesof Parma and ReggioEmilia(NorthernItaly) showingthe monitored locations. The dotted line roughly divides the territory into two regions, plain in the north, hills and mountains in the south.

the canisters during the exposure, could be measured by counting the gamma rays emitted by these two radionuclides (295 keV, 352 keV of Pb-214; 609 keV of Bi-214) for 30 min after a minimum waiting period of 3 h after the end of the exposures (George, 1984). Measurements were made with a gamma spectrometer (EG and G Ortec, USA) equipped with 162 cm 3 Ge(I) and 7.6 x 7.6 cm NaI(T1) detectors, coupled to an Ortec Adcam-918 multichannel buffer. The system was calibrated by impregnating the carbon contained in one canister, using a standard Ra-226 solution provided by Amersham, UK. After a 40-day period, the radon and daughters were in equilibrium with Ra-226; Pb-214 and Bi-214 had the same activity as Ra-226. A second calibration was necessary to correct for the adsorptivity of the charcoal for water instead of radon. Also a correction was applied for the differing exposure times of the canisters. Both of these corrections are specific for the

56

A. MALANCA ET AL.

batch of carbon used in the measurements and were obtained from the gamma spectrometric measurements of the Ra-226 standard. Slabs of bricks were crushed into small pieces and dried in an air circulation oven at 110°C for 24 h. Typically, 100 cm a of sample were weighed and stored in polyethylene sealed containers. After a 30-day period, the time necessary to allow the build-up of radon daughters, the samples were counted using a germanium detector. Radium-226 and Th-232 were assessed through their daughters photopeaks; Pb-214 (259 keV, 352 keV) and Bi-214 (609 keV); Ac-228 (911 keV) and TI-208 (583 keV, 2615 keY). Potassium-40 was measured directly via its 1461 keV peak. A homemade standard, QCY.44, contained a known mixture of nine radionuclides provided by Amersham, UK, and was used for calibration. RESULTS The results carried out in castles and other ancient buildings are listed in Table 1; sites are indicated in Fig. 1. Many of the sites are occupied during the holidaY season. Radon concentrations are expressed in Bq m -3. The values range from 8 Bq m -3 (Compiano castle) to 308 Bq m -3 (Contignaco castle). Specific activities of Ra-226, Th-232 and K-40 in bricks of Sala Baganza (XVIII century), Torrechiara (XV century), Roccabianca (XIV century) and Scipione (XIV century) are shown in Table 2, together with those for samples of modem bricks. The radionuclide content of old bricks appears to be slightly less than in modem bricks. DISCUSSION Most of the castles were built during the Middle Ages utilizing materials manufactured locally. For the construction of many baroque palaces, e.g. Colorno and Sala Baganza, 'recycled' bricks of earlier dilapidated castles were widely used. It is interesting to point out that in plain regions, castles and palaces are made only of bricks, whereas in mountainous regions, walls are made of bricks and squared sandstones. The lithological characteristics of the sites are grouped in Table 3. Precipitation and barometric pressure changes influence the indoor radon content in two ways; determining the availability of radon produced in soil and affecting the strength of driving forces for radon migration. Water blockage of the interpore openings normally impedes movement by both molecular diffusion and convection of radon-bearing soil gas (Tanner, 1989). On the other hand, Nazaroff and Doyle (1985) showed that heavy rainfall could enhance radon flux into a house. Temperature changes are also important; Arvela et al. (1988) demonstrated that in a group of Finnish houses, the

No. 9 11 12 21

18 17 23

20 1 2 3

Place

San Secondo Sissa

Noceto Montechia-

Rugolo Torrechiara

Felino

Rossena

Compiano Scipione

Bargone

Tabiano

Keep Room Room (NW) Room (E) Room (W) Room (N) Great hall (S) Room (N) Chapel

Keep (W) Great hall (SE) Room (SW) Room (N) Room (S) Room

Room Room (SW) Keep (N) Keep Great hall (E)

Location

XVI

XIV

X IX XIV XV XIII

XIV

XII

XII XV

XVI XVIII XIV XV XV

Castles Century

71 8 260 154 138 209 38 41 31

122 165 49 27 104 25

28 31 61 27 71

Rn*

1 2 g 1 g g ! 1 g

2 g 1 g g g

1 2 3 3 1

Floor

N Y N Y Y Y N N Y

N N Y N N N

Y Y N N Y

Frescoes

Dining-room Lounge Empty

Museum (a),(e) Bedroom (f) Lounge Empty

td)

Open for sightseeing

Office Office Archives (b) Empty Open for sightseeing Empty Open for sightseeing Empty (c)

Present use

Concentrations of radon inside 24 castles and 13 ancient buildings in the provinces of Parma and Reggio Emilia. Location refers to setting in which canisters were placed. Orientation in parentheses is given to better distinguish rooms in the same building. Numbers identify the places in Fig. 1. *, Bq/m3; (g), ground floor; (a), two measurements; (b), double-glazed window; (c), room with open fireplace; (d), castle built on a ophiolite rock; (e), stone walls; (f), castle built over an underground river; (h), castle built upon an underground cistern; (i), broken window panes; (k), castle built on a massive hard sandstone; (1), room with linoleum covered floor; (m), room with wooden floor; (n), walls with original plaster

TABLE 1

~o

~_ rz

Z -t

> z

z

O

g

5 22 10 7 13 16 8 19 26 27 28 30

15

Pellegrino BianeUo

Roccabianca Soragna

Varano Sala Baganza Fontanellato

Ravarano

Novellara

Arceto Scandiano Montericco

Other buildings Parma Pilotta Palace

University Palace Bishop Palace Synagogue

4

No.

Contignaco

Place

TABLE 1 (continued)

hall (S) (E)

hall (N) (W)

Room (S) Room (W) Room Room Room Synagogue

Room Great Room Room Room Great Room Room

Keep (NE) R o o m (S) Chapel Great hall (SW) Keep (W) Room Room (E) Bedroom (W) Room Room Room

Location

XVII XVI XVI XII XIX

XVI XV XIV XIV XIV

XIII

X XVI XI XIV XVII XIV XIII XVII XV

XIV

Castles Century

40 47 18 27 28 20

286 13 33 92 41 18 80 40

308 108 129 28 31 71 48 91 28 11 49

Rn*

2 1 g g 1 2

g l 2 g g g g 1

g g 1 1 1 g 1 g 1 l g

Floor

Y N N N N N

N Y N Y N Y N N

N N Y Y Y N Y Y N Y y

Frescoes

Office Library Office (1) Office (m) Empty (n)

Storehouse (i) Open for sightseeing (c) Bedroom (k) Empty (i) Open for sightseeing Pantry Dwelling Archives Library Restaurant Dwelling Dwelling (n)

Empty Dwelling

Dwelling (h)

Present use

San Vincenzo Palace Private house Gualtieri Bentivoglio Palace Gombio Parsonage

Reggio Emilia Bordello Tower

Bardi Fortress (d)

Sala Baganza Apoteosi Palace Colorno Aranciaia Palace Ducal Palace

29

25

24

14

16

(NW) (E) (E) (SW) (NE)

Room

Room (S) Great hall (W)

Room Room (W) Sacresty (S) Den

Room

Guard Room Room Tower Room

Room (N)

Room Throne room (E)

Room

XV

XVI

XII XIII XVIII XVII XVII

XIII XV XVI XVI XII

XVIII XVII

XVIII

29

19 31

27 15 22 36 92

43 28 61 177 228

136

66 75

13

N

Y Y

N N Y N N

N Y Y Y N

N

N Y

Y

Empty

Open for sightseeing

Dwelling

Office Empty Office

Empty (i) Museum Museum Museum (a) Empty

Museum Open for sightseeing, Office

Empty (i)

7`

7'

z

-t

...]

7` ¢'3 O 7`

60

A. MALANCA El" AL.

TABLE 2 Specific activities of Ra-226, Th-232 and K-40 in brick samples of modem and ancient buildings Place

Century

Ra-226 (Bq/kg)

Th-232 (Bq/kg)

K-40 (Bq/kg)

Scipione Roccabianca Torrechiara Sala Baganza Parma

XIV XIV XV XVIII XX

33 38 46 49 49

33 40 59 49 54

616 714 822 928 941

winter/summer concentration ratio could vary by a factor of ten. Even the radon exhalation rate of building materials can vary considerably with environmental parameters such as pressure, temperature and moisture content. As we performed the measurements in winter (dry season) and in spring (rainy season), the results are representative only for that period of the year. In Fig. 2 the mean radon concentrations in castles, ancient and modern buildings in the provinces of Parma and Reggio Emilia are plotted against the century of construction. The last column in the histogram refers to a series of - 1 5 0 measurements recently carried out, using the same method during the cold season, in private residences of Parma (Dallara et al., 1989) and Reggio Emilia (Malanca et al., 1991). The mean radon levels in castles and ancient buildings; 72 Bq m -3 (arithmetic mean) and 49 Bq m -3 (geometric mean) are higher than the values relative to houses built in the present and in the last century; 30 Bq m -3 (arithmetic mean ) and 19 Bq m-3 (geometric mean). Oscillations in observed radon concentrations may be accounted for by the variable percentage of measurements taken in ground floors in each group of buildings. Abu-Jarad and Fremlin (1982) noted that due to subsoil emanation, ground floor rooms showed more radon daughter activity than the first floor rooms even when the ventilation rate in the former was higher than in the latter. The results given in Table 4 for arithmetic and geometric means of radon concentrations are related to the distance of the story from the ground. In Table 5 the radon concentrations exhibit similar values for inhabited, used or empty settings indicating that the ventilation velocity should be more or less independent from the occupancy. The windows were generally old, sometimes in bad repair and nearly always kept closed. The slight difference between the two geometric means may depend upon a larger number of broken panes in empty rooms (3) than in those which are used (1).

61

RADON CONCENTRATIONS IN ANCIENT BUILDINGS

TABLE 3 Lithological characteristics of the sites. Numbers identify the sites in Fig. 1. Sites

No.

Lithological characteristics

San Secondo Soragna Fontanellato Parma Arceto Sissa Roccabianca Colorno Novellara Gualtieri Reggio Emilia

9 7 8 15 27 11 10 14 26 25 24

CoUuvial and alluvial deposits

Felino Montechiarugolo

17 21

Sands and conglomerates

Contignaco

4

Noceto Scandiano Sala Baganza Montericco Bianello Tabiano Slcipione Bargone Compiano Gombio Torrechiara Pellegrino Varano Ravarano Bardi

12 28 16 30 22 3

Rossena

23

Marls, marly clays, sandstones and limestones

2 20 29 18 5 13 19 6 Ophiolites

M e a n r a d o n levels w e r e less in f r e s c o e d c o m p a r e d with o r d i n a r y r o o m s . A c c o r d i n g to J o n a s s e n a n d M c L a u g h l i n (1980) the e x h a l a t i o n rate p e r unit a r e a (Bq m -2 h -~ w h i c h b o t h surfaces o f a wall are able to exhale into a r o o m m a y be w r i t t e n as E = efL tanh

(d/2L)

62 Bq

A. MALANCA ET AL.

m -3

11o

105 101

90

,IH 87

89 73

74 5C

7O 60

63

•

5O

47 45

30-

30

30

XVIII XIX

XIX XX

100

0 IX-X XI

pO

43

09

55

20

XII

XIIi

XIV

XV

XVI

XVII

century

Fig. 2. Arithmetic ( ) and geometric mean (A) radon concentrations in ancient and modern settings versus century of construction. Top numbers on each bar represent the arithmetic average and SD; bottom number gives the percentage of ground floor measurements.

where e = porosity o f the material, f = radon production rate (Bq m -3 h - l ) , L = diffusion length (m) and g = wall thickness (m). Setting L = 0.2 m (Stranden, 1988), assuming a typical wall thickness d = 0.2 m for modern buildings and d = 1 m for castles and considering that porosity and radon production rate are the same in both cases, gives E(ancient wall) ---- 2 X E(modern wall) TABLE 4 Arithmetic means (AM), standard deviations (SD) and geometric means (GM) of radon concentrations in castles and ancient buildings as a function of the distance from the ground Floor

No.

A M -4- SD (Bq/m 3)

GM (Bq/m 3)

Ground First Second and third

25 27 10

104 ± 88 52 ± 41 42 ± 32

71 41 32

63

RADONCONCENTRATIONSIN ANCIENTBUILDINGS TABLE 5

Comparisons of arithmetic means (AM), standard deviations (SD) and geometric means (GM) of radon concentrations in (a) inhabited or used settings versus void settings; (b) frescoed versus ordinary rooms. Number of ground floor measurements in parentheses Setting

No.

A M ± SD (Bq/m 3)

GM (Bq/m 3)

(a)

46 16 28 34

71 73 61 81

50 46 42 56

(b)

Inhabited or used rooms Empty rooms Frescoed rooms Ordinary rooms

(41) (43) (29) (50)

-F + ± ±

69 69 53 79

Owing to the larger mass of the walls, whose thickness ranges from 0.8-3 m or more, the radon contribution due to building materials is higher in ancient buildings than in modern ones. In the preceding equation only transport by pure diffusion is considered, however when gaps or cracks are present convection becomes the dominant mechanism. A likely possibility is that radon may flow through the bulk of the walls driven by the pressure differential across the building shell and the inner space of the house. An architect, experienced in historical monuments conservation, drew our attention to the structure of ancient buildings. In castles and antique palaces walls were made with a double layer of bricks filled with mortar and stones having sometimes large voids within them; numerous gaps and cracks in the structure can be produced by relatively frequent earthquakes and ground packing providing the radon with an easy way to infiltrate. Cliff et al. (1987) studying measures to reduce radon level in a building which was 100 years old, observed that a very important path by which radon from soil can enter the house appeared to be via the load-bearing walls. The most striking data emerging from Table 6 are the discrepancies between values relative to castles and other ancient buildings. These differences can be accounted for by the smaller number of ground floor measurements (30% in buildings, 46% in castles), or by the better conditions of plasters and walls in palaces. This last consideration can also explain the relatively low radon levels in buildings constructed during the latest two centuries. Factors affecting the final radon concentrations in ancient and modern buildings may be summarized as follows.

Ancient buildings Old briok and stone walls with numerous gaps and cracks; absence of any

64

A. MALANCA ET AL.

TABLE 6 Comparisonsof arithmeticmeans (AM), standard deviations(SD) and geometricmeans (GM) of radon concentrations in castles versus other ancient buildings Kind

No.

AM 4- SD (Bq/m3)

GM (Bq/m3)

Whole set Castles Other buildings

39 23

81 4- 75 56 4- 54

55 40

Ground floors Castles Other buildings

18 7

117 4- 90 72 4- 74

84 46

structure to prevent entrance of gas and moisture from the soil; bad weather stripping - high ventilation rate; numerous open fireplaces (venturi effect); prevalence of rooms on ground and first floor.

Modern buildings New brick and concrete walls; sometimes building materials with unusual high radium content may have been used; good insulation from the ground; new or double pane w i n d o w s - low ventilation rate; efficient heating systems (stack effect); prevalence of fiats in high -rise buildings (in Italy). Some of these characteristics promote an increase in radon build-up while others hinder this accumulation. Most of the factors counterbalance each other, but the lack of structures to prevent radon entry from soil within the presence of voids and cracks in old walls, results in radon concentrations which are higher in castles and ancient buildings than in modern houses. ACKNOWLEDGEMENTS We would like to thank the mayors of San Secondo, Sissa, Noceto, Compiano, Fontanellato, Colorno, Bardi, Novellara, Gualtieri and all proprietors who allowed us to leave the dosimeters in their castles and palaces. Dr. Emanuela Colombi, Mr. Diego Fontanesi, Mr. Giuseppe Conti, Mr. Maurizio Pontremoli and Mr. Riccardo Necchi are recognized for voluntary contribution. Special thanks to Dr. Gloria Fanigliulo for the linguistic revision.

RADON CONCENTRATIONS IN ANCIENT BUILDINGS

65

Finally we are grateful to Dr. Luciano Summer of Soprinten-denza per i Beni Architettonici of Parma for his valuable explanations about ancient buildings. REFERENCES Abu-Jarad, F. and J. Fremlin, 1982. The activity of radon daughters in high rise buildings and the influence of soil emanation. Environ. Int., 8: 37-43. Arvela, H., A. Voutilainen, I. Makelainen, O. Castren and K. Winkvist, 1988. Comparison of predicted and measured variations of indoor radon concentration. Radiat. Prot. Dosim. 24: 231-235. Castren, O., A. Voutilainen, K. Winkvist and I. Makelainen, 1985. Studies of high indoor radon areas in Finland. Sci. Total Environ. 45: 311-318. Cliff, K.D., A. Wrixon, J. Miles and P. Lomas, 1987. Remedial measures to reduce rayon concentrations in a house with high radon levels. In: P.K. Hopke (Ed.), Radon and its Decay Products. American Chemical Society, Washington DC, pp. 536-559. Cohen, B.L., 1987. Survey of radon levels in homes in the United States. In: P.K. Hopke (Ed.), Radon and its Decay Products. American Chemical Society, Washington DC, pp. 462-474. Cohen, B.L. and E.S. Cohen, 1983. Theory and practice of radon monitoring with charcoal adsorption. Health Phys., 45: 501-8. Dallara, G., F. Franchini, A. Malanca, M. Manfredi and V. Pessina, 1989. Measurements of radon-222 concentration in dwellings in Parma. Boll. Chim. Igien., 40: 79-85, in Italian with abstract in English. George, A.C., 1984. Passive, Integrated measurement of indoor radon using activated carbon. Health Phys., 46: 867-72. George, A.C. and L. Hinchliffe, 1987. Measurements of radon concentrations in residential buildings in the eastern United States. In: P.K. Hopke (Ed.), Radon and its Decay Products. American Chemical Society, Washington DC, pp. 42-62. Gesell, T.F., 1983. Background atmospheric Rn-222 concentrations outdoors and indoors: a review. Health Phys., 45: 289-302. Jonassen, N. and J. McLaughlin, 1980. Exhalation of radon-222 from building materials and walls. In: T.S. Gesell and W.M. Lowder (Eds.), Natural Radiation Environment III. US Dept. of Energy CONF-780422, pp. 1211-1226. Malanca, A., R. Orlandini, V. Pessina and G. Dallara, 1991. Radon in dwellings in Reggio Emilia. Acqua Aria, 1: 25-29, in Italian with abstract in English. Nazaroff, W.W., B.A. Moed, R.G. Sextro, K.L. Revzan and A.V. Nero, 1985. Factors influencing soil as a source of indoor radon: framework for assessing radon source potential. Report LBL 20645, Lawrence Berkeley Laboratory, Berkeley, CA. Nazaroff, W.W. and S.M. Doyle, 1985. Radon entry into houses having a crawl space. Health Phys., 48: 265-281. Nero, A., M. Boegel, C. Hollowell, J. Ingersoll and W. Nazaroff, 1983. Radon concentrations and infiltration rates measured in conventional and energy-efficent houses. Health Phys., 45: 401-405. Stranden, E., 1987. Radon-222 in Norwegian dwellings. In: P.K. Hopke (Ed.), Radon and its Decay Products. American Chemical Society, Washington DC, pp. 70-83. Stranden, E., 1988. Building materials as a source of indoor radon. In: W.W. Nazaroff and A.V. Nero (Eds.), Radon and its Decay Products in Indoor Air. American Chemical Society, New York, pp. 113-130.

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Swedjemark, G.A., 1980. Radon in dwellings in Sweden. In: Proc. from Nat. Radiat. Environ. III. Texas 1978, CONF-780422, pp. 1237-1259. Tanner, A.B., 1989. The source of radon in houses. In: N.H. Harley (Ed.), Radon Proc. 24th Annu. Meeting Natl. Counc. Radiat. Prot. Meas., Washington, DC, March 30-31, 1988. Proc. Ser. 10: 159-168. Wolfs, F., H. Hofstende, R. De Meijer and L. Put, 1984. Measurements of radon-daughter concentrations in and around dwellings in the northern part of the Netherlands; a search for the influence of building materials, construction and ventilation. Health Phys., 47: 271-279.