Pergamon Appl. Radiat. lsot. Vol. 46. No. 12, pp. 1387-1392, 1995

Copyright © 1995 Elsevier Science Ltd 0969-8043(95)00223-5 Printed in Great Britain. All rights reserved

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Natural Radioactivity in Building Materials from the Brazilian State of Espirito Santo

A L B E R T O 1, M A L A N C A , V A L E R I O P E S S I N A 2, G I U S E P P E D A L L A R A 2, C Y N T H I A N E W B Y L U C E 3 and L A U R A G A I D O L F I 4

~Dipartimento di Fisica, Universith Degli Studi di Parma, Viale delle Seienze, 43100 Parma, Italy 2Settore Fisico-Ambientale, PMP-USL No. 4, Via Spalato 4, 43100 Parma, Italy

3Conselho Municipal da Preserva¢o do Patrimnio Histrrico, Artistico e Cultural, 25780 970 S~o Jos6 do Vale do Rio Preto, Rio de Janeiro, Brasil

4Settore Fisico-Ambientale, PMP-CRR, Via XXI Aprile - 48, 29100 Piacenza, Italy

(Received 27 January 1995; in revised form 14 April 1995)

In order to assess the radionuclide content of building materials utilized in the towns of Guarapari and Meiaipe, located in the Brazilian state Espirito Santo, 48 samples of raw materials and construction products were collected and shipped to our laboratory in Italy. Here, concentrations of background radionuclides in samples were determined by v-ray spectroscopy with two HPC_re detectors. The radium- equivalent activity concentrations in the samples varied between 14.6 (sand) and 1930 Bq kg -~ (plaster).

Introduction

It has now been firmly established that mankind's exposure to radioactivity comes mainly from natu- ral sources. The natural radiation to which the pub- lic is exposed consists mainly of two distinct components, namely: the internal exposure origi- nated from radionuclides in diet and from radon gas breathed in the air, and the external exposure generated both by cosmic rays and ),-rays given off by radioactive elements in soils, rocks, and building materials.

The staple source of the external exposure in dwellings is caused by members of uranium and thorium decay chains and by 4°K incorporated in construction materials. Raw and processed building products can vary considerably in radionuclide con- tent according to the geological conditions at the site of production (Schuler et al., 1991). In the past two decades, considerable attention has been given to low-level exposure arising from 226Ra, 232Th and 4°K contained in building structures. The specific activity of many materials has been assessed in sev- eral countries, and various products with relatively high levels of radioactivity have been identified (Nero and Nazaroff, 1984). For instance, the ac- tivity concentration (sometimes referred to as the specific radionuclidic activity) of 226Ra in Swedish

*To whom all correspondence should be addressed.

aerated concretes averaged 1300 Bq kg- (Swedjemark, 1980).

Although the knowledge of radioactivity levels in dwellings is important for the estimate of possible radiological hazards to human health, no surveys, or at least very few, have been conducted in devel- oping countries. In Brazil, the most populous nation of all South America, data for building materials for one of its northeastern states (Rio Grande do Norte) have recently been published (Malanca et al., 1993a); however, analogous infor- mation concerning high-background Brazilian areas are not easily traced in the literature.

The most important anomalies in the concen- tration of naturally occurring radionuclides in soils of that country have been reported in two areas. The first one is the zone of volcanic alkaline intru- sires in the states of Minas Gerais and Goias; the second is the belt of monazite sand along the Atlantic coast in the state Espirito Santo (ES). The geology of this last area has been described exhaus- tively by many authors and reviewed by Roser et al. (1964). According to these studies, decomposition and weathering of the archeognaisses in the pre- Cambrian mountains paralleling the Atlantic shore produced, in geological times, a natural separation and concentration of very water-insoluble minerals such as zircon, ilmenite and monazite. As a result, deposits of strongly radioactive minerals are aligned in almost continuous succession for over 500 km

1387

1388 Alberto Malanca et al.

Minas G e r a i ~ A~ L~natni c

:0. / /

~. ~rrGuarapari ) S Meiaipe ~ _ J 0 50km

Rio de Janeiro~ 4[ ' I '

Fig. 1. Map of Espirito Santo (Brazil) showing the towns surveyed.

along the coast of ES. The monazite in beaches of this state may reach, even over considerable extension, a concentration of 0.5%. In several patches of black sand (in Brazil these spots are called "areia preta") the concentration of this radio- genic mineral, a complex of rare earth phosphates with 0.15--0.25% uranium oxide and 4--6% thorium oxide, ranges from 5 to 20*/0.

In Asia, deposits of this radioactive mineral have been recently confirmed in the beaches of Cox's Bazar of Bangladesh, where monazite sand was probably merged in certain building masonry ma- terials (Mollah et al., 1986).

This work reports the results of ~,-ray spectro- metric measurements performed on 48 samples of building materials collected in the coastal towns of Guarapari and Meiaipe in ES (Fig. 1). These two vacation towns were chosen since they had already been surveyed by Brazilian scientists and were recognized as the most radioactive of the whole region (Penna Franca, 1977). Furthermore, local lores have it that "areia preta" gives off energy rich with beneficial effects and every year thousands of tourists travel for long distances to spend their holi- days on the black sands of these resorts. Our inter- est has been heightened by the considerations of investigators who, without any evidence, hypoth- esized the stray use of black sand as raw material in the local construction industry (Roser and Cullen, 1964; CuUen, 1977).

Materials aml Methods

A total of 48 samples of sand, mortar, plaster, concrete, floor, roof tile and brick were collected for the measurements of activity concentrations. These materials were gathered directly in demol- ished houses, churches, rubble piles or buildings

under construction (nine sites at Guarapari and one site at Meiaipe, which lie only a few km apart). Detailed identifications of the materials examined are as follows:

1. Samples ES01, ES13, ES26, ES36, ES37 from an apartment house under construction at Guarapari (Gp).

2. Samples ES03, ESI2, ES24, ES31, ES47, ES48 gathered in an apartment house under construction at Meiaipe. ES12 comes from Santa Monica (8 km from Gp), ES48 from Jabaqui~aba (30 km from Gp), and ES03 from Barra de Jacu (10 km from Gp).

3. Sample ES32 from a new kiosk near the sea at Gp.

4. Samples ES06, ES07, ES27 taken from a church built in 1585 and still in use at Gp. ES08, ES09, ES28, ES33 from a rubble pile by this church.

5. ES10, ES16, ES29, ES30, ES34 from a stone church (in disrepair) built in 1677 at Gp.

6. Samples ES17, ES18, ES19, ES20, ES41 from an old house abandoned at Gp.

7. Samples ESll , ES21, ES35, ES42, ES43, ES44 from a ruined house at Gp.

8, Sample ES25 from an old, abandoned kiosk (in disrepair) on the beach of Gp.

9. Samples ES02, ES04, ES05, ESI4, ES15, ES38, ES39, ES40 collected in a remodeling house at Gp. ES02 comes from Morro Beach at Setiba (15 km from Gp). 10. ES22, ES23, ES45, ES46 from a cemetery wall at Gp.

Solid samples were crushed into about 5 mm par- ticles; wet samples were dried for 24 h in an air-cir- culation oven at 110°C. Typically, an aliquot of 100 cm 3 of each sample was weighed and stored in a 100 cm 3 polyethylene container for a 40-day ingrowth period. These containers were sealed after closure so that 222Rn and 22°Rn could not escape.

226Ra and 232Th were assessed from the intensity of the v-ray lines of their daughters: 214pb and 21aBi; 22SAc and 2°STl; 4°K was measured directly via its 1461 keV peak. The 186 keV peak from 226Ra itself was not utilized since the 185.7 keV peak from 238U would have overlapped with the same y-ray line. In this investigation the concen- trations of 238U and other 226Ra precursors were ignored since 98.5% of radiological effects of the uranium series are produced by radium and its daughter products. Measurements were made with two different detectors (EG&G Ortec, U.S.A.); sig- nals from each detector were fed into an Ortec Adcam 918 multichannel buffer. For 36 samples we used a v-ray spectrometer furnished with a 162 crn 3 HPGe detector whose energy resolution of the 1332 keV line from 6°Co v-rays was found to be 1.75 keV at FWHM with a relative efficiency at 1.33 MeV of 26.6%. For 12 samples we used a spec- trometer equipped with a 55 c m 3 HPGe coaxial

Radionuclides in Brazilian building materials 1389

detector with the same characteristics of the other crystal, but with a relative efficiency of 82.5%.

A standard contained a known mixture of nine radionuclides (Amersham, U.K.) and was used for calibration of both the detectors, which were sur- rounded by 10-cm lead shields with internal walls of electrolytic copper and cadmium. A computer program, matching recorded photopeaks to a library of possible isotopes, was employed for spec- troscopy analysis. The same geometry was used for each sample (as well as for the standard), using a counting time of 86,400 s. In order to determine the background distribution due to naturally occurring radionuclides in the environment around the detec- tor, an empty polyethylene container was counted in the same manner as the samples. Self-adsorption of the 7-radiation by the samples was found to be negligible.

For completeness, the content of primordial radionuclides in 19 samples of black and normal sands taken on the beaches of Guarapari and Meiaipe was determined with the same procedure used for the building materials.

The overall uncertainty in the determination of the activity of the radionuclides, taking into account the statistical uncertainty and the cali- bration uncertainty (1.8%), varied between 5 and 10%, at 95% confidence level. As usual for environ- mental samples analyzed in our laboratory, the con- centration of the manufactured radionuclide 137Cs

was also assessed for all the collected materials.

R e s u l t s

The preliminary survey of the specific activities of radium and thorium in sandy samples revealed

that the activity concentration of 226Ra ranged from 1.3 to 16.0 Bq kg - t , with a geometric mean (GM) of 3.7 Bq kg - t in nine samples of normal sand and 25.3-2412 (GM=431 Bq kg - I ) in 10 samples of black sand. The corresponding values for 232Th were 2.3-93.3 Bq k g - l ( G M = 1 5 . 0 Bq kg - l) in normal sands and 189.5-36,620 Bq kg -~ (GM = 4870 Bq k g - l ) in black sands. All these data are presented in Fig. 2, where the analogous values for 51 soil samples from the Brazilian state of Rio Grande do Norte (Malanca et al.. 1993b) are also depicted for comparison.

The activity concentrations of naturally occurring radionuclides in 48 samples of building materials gathered at Guarapari and Meiaipe are listed in Table 1. It may be seen that 226Ra activity concen- tration oscillates between 5.7 and 117.5 Bq kg - l , whereas that of 232Th varies between 3.5 and 1256 Bq kg -1. In order to compare the specific activities of materials containing different amounts of radium, thorium and potassium, an index, Ra(eq), called the radium-equivalent activity concentration, is also presented in Table 1. This index is defined as :

Ra(eq) = (A/m)R a + [1.43 × (A/m)Th]

+[0.077 × (A/m)K],

where (A/m)Ra, (A/m)Th and (A/m)K are the activity concentrations of 226Ra, 232Th and 4°K respectively, in Bq kg -1 (NEA-OECD, 1979). This equation is based on the estimate that 1 Bq k g - l of 226Ra, 0.7 Bq k g - ] of 232Th or 13 Bq k g - I of 4°K generate

the same 7-ray dose rate. As a rule, the use of materials whose radium-equivalent activity concen-

I x [ Th

x

i x [ Ra

x ] Ra

I Ra

]Th

I I I I J i l l J ] I I [ ] i l l ] I [ ] ] i l l [ [ i I ] I ] i l l i

10 10 2 10 3 10 4

B q k g - ]

226 232 Fig. 2. Distribution of the activity concentrations of Ra and Th in normal sands (a), (b) and black s a n d s (e), (f) collected at Guarapari and Meiaipe. As a comparison, the range of values of 226Ra and 232Th activity concentrations in soils of 51 sites of the Brazilian state Rio Grande do Norte (c), (d) are

also depicted. ( x ) = geometric mean.

I T,

I I

1390

Table 1. Radionuclide

Alberto Malanca et al.

activity concentrations and radium-equivalent activity concentrations of building materials used at Guarapari and Meiaipe in the Brazilian state of Espirito Santo

Code Material 226Ra (Bq kg-l) 232Th (Bq kg -I) 4°K (Bq kg-l) Ra(eq) (Bq kg- ' )

ES01 a Sand 19.1 75.8 52 113.5 ES02 a Sand 5.7 7.6 51 20.5 ES03 a Sand 5.8 3.5 49 14.6 ES04 a Mortar ! 3.2 48.2 123 91.6 ES05 a Mortar 12.2 19.3 63 44.6 ES06 Mortar 9.6 23.8 82 49.9 ES07 Mortar 14.1 12.8 21 34.0 ES08 Mortar 68.8 701.5 141 1082.8 ES09 Mortar 44.7 215.6 1823 493.4 ES 10 Mortar i 8.7 15.2 69 45.7 ESI1 Mortar 18.9 104.8 104 176.8 ESI2 a Mortar 17.7 31.6 ND 62.9 ES 13 a Plaster 15.9 32.5 71 67.8 ESI4 a Plaster 11.9 18.6 108 46.8 ES 15 a Plaster 17.5 29,7 73 65.6 ES16 Plaster 22.3 83.6 323 166.7 ES17 Plaster 24.3 73,1 145 140.0 ESI8 Plaster 75.3 744,8 146 1151.6 ES 19 Plaster 40.9 264.9 94 426.9 ES20 Piaster 117.5 1256 211 1930 ES21 Plaster 14.9 77.0 91 132.0 ES22 Plaster 8.9 38.1 11 63.4 ES23 Plaster 17.6 50.5 115 98.7 ES24 ~ Plaster 13.4 12.7 ND 31.6 ES25 Floor 8.5 51.8 56 86.9 ES26 a Concrete 26.0 12.0 100 50.9 ES27 Concrete 21.9 32.2 71 73.4 ES28 Concrete 17.6 22.6 12 50.8 ES29 Concrete 23.1 19.2 75 56.3 ES30 Concrete 10.3 21.8 371 70.0 ES 31 a Concrete 20.5 15.3 ND 42.4 ES32 ~ Concrete 34.0 119.6 95 212.3 ES33 Roof tile 59.5 144.6 372 294.9 ES34 Roof tile 65.3 85.7 359 215.5 ES35 Roof tile 44.0 67.0 509 179.0 ES36 a Brick 70.2 126.2 397 281.2 ES37 a Brick 69.8 99.0 435 244.9 ES38 ~ Brick 41.0 91.2 234 189.4 ES39 ~ Brick 43.6 88.0 396 199.9 ES40 a Brick 36.0 75.2 407 174.9 ES41 Brick 28.2 78. l 259 159.8 ES42 Brick 26.9 104.6 149 187.9 ES43 Brick 52.6 74.0 553 201.0 ES44 Brick 36.7 75.7 ND 144.9 ES45 Brick 53.8 147.8 403 296.2 ES46 Brick 82.0 488.6 155 792.6 ES47 a Brick 9.5 12.7 286 49.7 ES48 a Brick 58.0 97.7 514 297.3

aSamples from new constructions; ND = not detectable.

t r a t i on exceeds 370 Bq kg - n is d i s c o u r a g e d

(Bere tka a n d M a t h e w , 1985). T h e act ivi ty c o n c e n t r a t i o n o f 137C8 was genera l ly

lower t h a n the m i n i m u m de tec tab le c o n c e n t r a t i o n

w h i c h is, for ou r sys tem, 1.5 Bq kg -1 . H o w e v e r ,

fou r samples s h o w e d a non-negl ig ib le ces ium ac-

tivity. They were th ree r o o f tile samples (ES33 wi th

2.6 Bq k g - ~ ; ES34 wi th 11.4 Bq k g - ~ ; ES35 wi th 4.4 Bq k g - l ) , a n d a br ick s amp le (ES43 wi th 6.3

Bq k g - l ) . This was an unexpec ted , surpr i s ing

result , as it was the very first t ime we f o u n d this

m a n - m a d e rad ionuc l ide in bu i ld ing mater ia ls .

U n f o r t u n a t e l y , we have n o scientific exp l ana t i on ,

excep t to sugges t a poss ib le c o n n e c t i o n wi th the

rad io log ica l acc iden t o f G o i n i a ( m o r e t h a n 1000 k m

away f r o m Esp i r i to San to ) where , in S e p t e m b e r 1987, a 137C8 te le the rapy source o f ~ 5 1 T B q was

v io la ted (Okuno , 1988; M a l e t s k o s a n d Lipsz te in ,

1991). N o n e t h e l e s s , an add i t i ona l c o n t r i b u t i o n f r o m earl ier w o r l d - w i d e fa l lout f r o m nuc lear tes ts shou ld n o t be exc luded a priori .

Discussion

The m i n i m u m r a d i u m - e q u i v a l e n t act ivi ty concen- t r a t i on (14.6 Bq kg - t ) was obse rved in a s ample o f s a n d (ES03) ut i l ized in a bu i ld ing ya rd at Meia ipe . T h e m a x i m u m Ra(eq ) (1930 Bq kg - 1 ) was n o t e d in

a p las te r s ample (ES20) col lec ted in an o ld a b a n - d o n e d co t t age a t G p . A be t t e r u n d e r s t a n d i n g o f the d a t a m a y be a t t a ined f r o m Tab le 2, whe re the m e a n values o f r ad ionuc l ide act ivi ty c o n c e n t r a t i o n s a n d Ra(eq) values for mate r ia l s o f ES are c o m p a r e d to the ave rage c o n c e n t r a t i o n s o f mate r ia l s co l lec ted in the s ta te R io G r a n d e d o N o r t e ( M a l a n e a et al. ,

1983a).

Radionuclides in Brazilian building materials 1391

Table 2. Mean radionuclide content and Ra(eq) in building materials of Guarapari and Meiaipe (Espirito Santo) and Rio Grande do Norte.

Material No. of samples 226Ra (Bq k g - t ) 232Th (Bq k g - i ) 4°K (Bq k g - i ) Ra(eq) (Bq k g - i )

Espirito Santo Brick 13 46.8 + 19.4 119.9+ 110.6 322+ 152 247.7_+ 170.3 Conctete 7 21.9 -t- 6.7 25.3 '~ 42 a 79.4 -I- 55.2 Mortar 9 24.2-+ 18.5 50.5 a 62 a 107.3" Plaster 12 31.7 -+ 31.2 78.0 a 116 -+ 83 149.0" Roof tile 3 56.3+9.0 99.1 +33.1 413-+68 229.8-+48.8 Sand 3 10.2-+6.3 12.6 a 51 -+ 1 34.0 a

Rio Grande do Norte Brick 9 50.7 _+ 18.9 69.4 + 26.2 728 -+ 243 206.0 -+ 66.9 Concrete 2 7.1 -+5.0 9.9:t: 1.6 360_+ 188 56.7-+ 17.2 Plaster 2 37.5 -+ 27.2 87.6-+ 73.4 649 -+ 553 212.8 _+ 174.8 Roof tile 3 51.1 _+ 1.2 95.6-t- 15.4 944_+64 264.5-+23.9 Sand 4 14.3_+5.3 180.0_+ 13.5 809_+ 141 102.2+23.3

aGeometric mean.

Most of the materials analyzed in our research showed low activity concentrations of 226Ra (GM=23.5 Bq kg - t ) and 232Th (GM=56.3 Bq kg-l) , comparable to those of materials from Rio Grande do Norte (GMRa=28.5 Bq kg- t ; GMTh=27.7 Bq kg-1), whereas the 4°K activities were generally lower than those of samples coming from the latter region. However, for two samples of mortar (ES08 and ES09), three of plaster (ES18, ES19 and ES20) and one of brick (ES46), all gath- ered in old structures, a value of Ra(eq)> 370 Bq kg-J was recorded. The high radium-equivalent ac- tivity concentrations observed in these six samples were always derived from conspicuous thorium con- tents. Furthermore, in the five most radioactive samples, the thorium-radium ratio ranged from 6.0 to 10.2 while, in less radioactive materials its value varied between 0.5 and 6.1. Sample ES09 was not considered for this comparison because about one- third of its Ra(eq) came from an extraordinarily high 4°K content (1823 Bq kg-1).

At any rate, the greater part of the samples, even those with a low Ra(eq), exhibited a thorium con- tent higher than the radium content (Fig. 3). This

fact reflects the normal pattern of many Brazilian soils, namely 232Th/226Ra>l (Pfeiffer et al. , 1981; Malanca et al. , 1993b). It is interesting to notice that for normal sands taken on the shore of the two towns this ratio ranged from 1.8 to 6.4, while in black sands its value varied between 5.1 and 15.2; it was also observed that the 232Th/226Ra ratio in sands was roughly proportional to the thorium content of the samples.

The abnormal thorium content together with the high 232Th:226Ra ratio, typical of black sands, found in some of our samples, support the con- clusion that variable amounts of radioactive sand were occasionally mingled with lime in order to produce plaster and mortar at Guarapari. This con- clusion was confirmed by a microscopical analysis of ES20. In this sample several crystals of ilmenite were observed along with numerous crystals of monazite (UO2:0.1-1%; ThO2: 5-10%).

C o n c l u s i o n s

The results of this research seem to prove the hypothesis that monazite sand was intentionally

I I -~ 1 I

I -" I I

[ I • I I

I © 1 [

I I I I I I I I 1 3 5 7 9 11 13 15

232Th/226Ra

Fig. 3. Activity ratios of 232Th and 226Ra in normal sands (a), black sands (b), high Ra(eq) building materials (c), and low Ra(eq) building materials (d) of Guarapari and Meiaipe. O~')= sample ES09;

(I-OI) = arithmetic mean + 1 SD,

1392 Alberto Malanca et al.

merged in building materials produced locally. Nonetheless, it is worth stressing that the radio- activity of most building materials from Guarapari and Meiaipe is similar to that of products ordinarily utilized in Europe and U.S. Only six samples out of 48 presented a relatively high radium-equivalent value, comparable for instance, to that of some Finnish by-product gypsum (Mustonen, 1984). On the other hand, the radium-equivalent activities found in building materials used for new construc- tions in these two towns are not particularly high. It is then reasonable to guess that the use, based on alleged beneficial effects, of mixing black sand to mortar and plaster is being abandoned. Luckily, the frantic urbanistic development of Guarapari and, to a lesser extent of Meiaipe, caused by an increasing touristic flow, is bringing about the demolition of many old single-family houses which are promptly replaced by modern dwellings. These tier buildings are mainly made with low-radioactivity products coming from inland industries; as a result, a decreasing fraction of inhabitants will receive a rela- tively high radioactive dose generated by monazite sand introduced in building materials.

Acknowledgements--The authors are particularly indebted to Dr Sandro Meli for his help with electron microscope. Special thanks are also due to Dr Gloria Fanigliulo for the linguistic revision of the manuscript.

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