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Journal of Environmental Radioactivity 132 (2014) 21e30

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Journal of Environmental Radioactivity

journal homepage: www.elsevier .com/locate/ jenvrad

222Rn, 220Rn and other dissolved gases in mineral waters of southeastBrazil

Daniel Marcos Bonotto*

Departamento de Petrologia e Metalogenia, IGCE e Instituto de Geociências e Ciências Exatas, UNESP e Universidade Estadual Paulista Júlio de MesquitaFilho, Av. 24-A, No. 1515 e CP 178, Bela Vista CP 178, CEP 13506-900 Rio Claro, SP, Brazil

a r t i c l e i n f o

Article history:Received 20 September 2013Received in revised form8 January 2014Accepted 10 January 2014Available online 14 February 2014

Keywords:Radon and thoronMineral watersDissolved gasesRadiation dose

* Tel.: þ55 19 35269244; fax: þ55 19 35249644.E-mail addresses: danielbonotto@yahoo.com.br,

com.

0265-931X/$ e see front matter � 2014 Elsevier Ltd.http://dx.doi.org/10.1016/j.jenvrad.2014.01.005

a b s t r a c t

This paper describes the natural radioactivity due to 222Rn and 220Rn in mineral waters occurring at SãoPaulo and Minas Gerais states, Brazil, that are extensively used for drinking in public places, bottling andbathing purposes, among other. The measurements of these alpha-emitting radionuclides were alsoaccompanied by the monitoring of temperature and some dissolved gases (O2, CO2 and H2S) in 75 watersources located in 14 municipalities of those states. Eight water sources yielded 220Rn activity concen-tration values below the detection limit of 4 mBq/L. On other hand, 222Rn activity concentration valuesexceeding the WHO guidance level of 100 Bq/L in drinking-water for public water supplies were found intwo springs, named Villela and Dona Beja, whose discharge occurs in areas characterized by the presenceof enhanced levels of natural radioelements in rocks. The obtained results were compared with theguidelines of the Brazilian Code of Mineral Waters (BCMW) that was established in 1945 and is still inforce in the country. The 222Rn and 220Rn activity concentration data allowed perform dose radiationcalculations based on the potential alpha energy concentration (PAEC), whose implications for health riskhave been also considered in this paper.

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1. Introduction

In many countries, spring waters have been extensively used forconsumption purposes as an option to tap water, as many peoplebelieve they are healthy and/or can be utilized for health cures.Additionally, economic reasons have also favored their use asbottled waters so that the commercialization of mineral waters haswidely increased.

The thermal andmineral waters use in Brazil is not recent due toarrival of European immigrants, mainly from Portugal. For instance,Gonsalves (1936) reported that the thermal waters occurrence inCaldas Velhas (Goiás State) was realized in 1722. The thermal spaswere gradationally constructed in Brazil for therapeutic and leisurepurposes, corresponding the period elapsed between the 1930s and1950s to the most auspicious hydrothermal period in the country(Mourão, 1992). The Brazilian Code of Mineral Waters (BCMW) wasestablished in this time, under French influence, by Register 7841published on 8 August 1945 (DFPM, 1966). This rule is still in forcewithout any actualization, focusing the mineral waters for spas andbottling uses, as well the potable waters for bottling (Serra, 2009).

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In Brazil, the production and commercialization of mineral wa-ters is managed by the National Department of Mineral Production(DNPM). Traditionally, the mineral waters had been used or directlyconsumed in the springs, where touristic centers developed around.However, in the present days, the mineral water for consumption isdistributed in vessels for ingestion distant from the springs, whereashydrothermal spas for therapeutic baths and leisure exhibit infra-structure with hotels and many facilities for users.

The first available information about the production of bottledmineral waters in Brazil dates back 1911 (CPRM, 2012). Only MinasGerais and Rio de Janeiro States had industries by that time, whoseannual production was 1,420,000 L (Minas Gerais- 1,220,000 L; Riode Janeiro- 200,000 L) (CPRM, 2012). However, an accentuatedexpansion of the national production occurred in the period be-tween 1996 and 2007, i.e. North region (þ386%), West Central re-gion (þ287%), South region (þ207%), Northeastern region (þ130%)and Southeastern region (þ127%) (CPRM, 2012). The Southeasternregion in 2007 was responsible by about 48% of the national pro-duction of mineral and potable water, the highest in the country(2.08 billion liters) (CPRM, 2012). São Paulo State presented aproduction superior to 1.5 billion liters in 2007, corresponding to34% of the total in the country, followed by the states of Rio deJaneiro (7%) and Minas Gerais (6%) (CPRM, 2012). In general terms,circa 20 million consumers are involved (SEBRAE, 2012).

Fig. 1. Sketch map of the research region in Brazil and location of the groundwatersampling points in the following cities of São Paulo and Minas Gerais states:ASP ¼ Águas de São Pedro, ADL ¼ Águas de Lindóia, SEN ¼ Serra Negra, LIN ¼ Lindóia,TEI ¼ Termas de Ibirá, ASB ¼ Águas de Santa Bárbara, ADP ¼ Águas da Prata, PDC ¼Poços de Caldas, PRV ¼ Pocinhos do Rio Verde, LAM ¼ Lambari, SLO ¼ São Lourenço,CAM ¼ Cambuquira, CAX ¼ Caxambu, AXA ¼ Araxá.

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e3022

Many spring waters in Brazil do not contain high concentrationsof dissolved constituents, but the waters are considered mineraldue to the radioactivity in them, chiefly due to the presence ofdissolved radon (222Rn) and thoron (220Rn) (DFPM, 1966). 222Rn(half-life 3.82 days) and 220Rn (half-life 55.6 s) are noble gas iso-topes belonging to the 238U (4n þ 2) and 232Th (4n) decay series,respectively. 222Rn is produced by a-decaying 226Ra and reaches thestable 206Pb, whereas 220Rn is generated by a-emitting 224Ra,forming the stable 208Pb (Clayton, 1983; Chu et al., 1999). Some222Rn and 220Rn fraction escapes from the rocks andminerals to thesurrounding fluid phase, such as groundwater and air, whose pro-portion depends on factors such as total surface area of solids andthe concentration (and distribution) of 238U (226Ra) and 232Th(224Ra) in them (Flügge and Zimens, 1939).

Potential health hazards from natural radionuclides inconsuming water have been considered worldwide, with manycountries adopting the guideline activity concentration for drinkingwater quality recommended by WHO (2011). In general, the rec-ommendations apply to routine operational conditions of water-supply systems, however, special attention must be also given tomineral waters frequently ingested by population. Thus, theapproach for radioactivity in the BCMW (DFPM, 1966) is contra-dictory to that focused by WHO (2011).

Another relevant aspect in this situation is the lack of confidentdata on the 222Rn and 220Rn activity concentration in Brazilianspring waters, mainly for 220Rn. The available 222Rn data in somecases is partially a consequence of the timescale of its half-life thatis longer than that of the 220Rn. This paper describes a comparativestudy of well-known Brazilian mineral waters occurring at SãoPaulo and Minas Gerais states that was held for evaluating thepresence of the following dissolved gases: 222Rn, 220Rn, O2, CO2 andH2S. With exception of oxygen, all other gases are taken into ac-count in the BCMW (DFPM,1966) that has been utilized on the dataevaluation. The radiation dose due to the presence of dissolved222Rn and 220Rn has been calculated as both radionuclides arehealth threat when ingested in water in activity concentrationsexceeding the guideline reference values.

2. Study area

The groundwater samples (75) for dissolved gases analysesweretaken from springs and pumped tubular wells drilled at differentaquifer systems that are inserted in Paraná and Southeastern Shieldhydrogeological provinces (Fig. 1 and Table 1).

Águas de São Pedro, Águas de Santa Bárbara and Termas de Ibirácities are inserted in the intercratonic Paraná sedimentary basin, inwhich the sedimentary sequence covers since the Silurian-Devonian up to the Cretaceous periods (IPT, 1981). The samplingpoint at Águas de Santa Bárbara city corresponded to a 120 m-deeptubular well that cut the Serra Geral and Botucatu formations of theParaná sedimentary basin. The waters of Águas de São Pedro cityprovided from tubular wells drilled at the Tubarão Group (Paranábasin) in 1936 by DNPM (National Department of Mineral Pro-duction) for petroleum exploration (Kimmelmann et al., 1987).However, such water sources have been popularly referred toGioconda (Tubarão Group depth ¼ 275e625 m), Juventude(Tubarão Group depth ¼ 240e469 m) and Almeida Salles (TubarãoGroup depth ¼ 207e329 m) “springs” (Kimmelmann et al., 1987).

Águas de Lindóia, Serra Negra and Lindóia cities are located in aregion characterized by the occurrence of several phases and cycles,involving different aspects of metamorphism, deformation andmagmatism that acted from the Archean to the Upper Proterozoictimes and affected rocks characterized by high metamorphic grade,generally of granulite and amphibolite facies (Ebert, 1955; Almeidaand Hasui, 1984). The water circulation at Águas de Lindóia city

generally realizes through fractures and the flow is from the higherto lower altitudes (del Rey, 1989), leaching migmatite (Lindália andSanta Isabel), quartzite (Comexim, Curie, Filomena and Beleza) andmilonite/quartzite (São Roque).

Águas da Prata, Poços de Caldas and Pocinhos do Rio Verde citiesare geologically situated in the Poços de Caldas alkaline complexthat is a ring structure of Mesozoic age, comprising a suite ofalkaline volcanic and plutonic rocks, mainly phonolites and neph-eline syenites (Schorscher and Shea, 1992). Seven springs weresampled at Águas da Prata city: Villela (discharges into a wellsilicified and lightly folded sandstone), Vitória (discharges throughfissures in diabase), Platina (discharges in outcropping phonolites),Prata (discharges in diabase), Boi (discharges in a silicified andrecrystallized sandstone), Paiol and Padre (discharges throughvolcanic tuffs, phonolites and eudialite-bearing nepheline syenites)(Szikszay, 1981). Groundwater at Poços de Caldas area has beenmainly exploited in crystalline fractured rocks due to the betteryielding of the wells, but it also occurs in diffuse and punctualthermal and non-thermal springs that discharge at the depressionin Poços de Caldas city (Cruz, 1987; Cruz and Peixoto, 1989).

The geological substrate of Lambari, São Lourenço, Cambuquiraand Caxambu cities in south ofMinas Gerais State comprises rocks ofthe Proterozoic times like ophthalmic biotite gneisses, migmatizedgranitoids, protomilonites and milonite gneisses, migmatizedgarnet-biotite-gneisses, metabasites intercalations secondarily cutby pegmatoids veins and schists. There is also the presence of veryweathered quartzites and Quaternary alluvial deposits (CPRM,1999).The hydrogeological model for mineral waters occurring in SãoLourenço, Lambari and Caxambu cities involves the rainwater infil-tration in weathered horizons of gneissic rocks at the more elevatedtopographic areas close to the springs (CPRM, 1999). Then, this issucceeded by percolation through milonitized zones (São Lourenço,Caxambu, and Lambari) and fractures partially filled by pegmatoids

Table 1Description of the groundwater samples analyzed in this paper.

City (Statea) Spring (well)name/Sample code

HydrogeologicalProvinceb

Dominant flow Major rock types Geological context/age Commercializationc

Águas de SãoPedro (SP)

Almeida Salles/ALS Paraná Porous Sandstones Botucatu Fm. (Jurassic)Gioconda/GIO Pirambóia Fm. (Triassic)Juventude/JUV Itararé Fm. (Permian)

Irati Fm. (Permian)

Águas daPrata (SP)

Platina/PLA Paraná Fractures Diabases Botucatu Fm. (Jurassic) YesPaiol/POL Phonolites Serra Geral Fm.

(Jurassic-Cretaceous)Vitória/VIT Alkaline rocks Poços de Caldas

intrusive complexBoi/BOI Silicified sandstones (Cretaceous)Prata/PTA YesVillela/VILPadre/PDE

Águas deLindóia (SP)

Santa Isabel/SIL Paraná Fractures Granites Amparo Gp.(Lower Proterozoic)

Yes

Filomena/FIL GneissesBeleza/BEL MigmatitesSão Roque/SRE SchistsComexim/COM Quartzites YesLindália/LIN Limestones YesCurie/CUR Dolomites

SerraNegra (SP)

São Jorge/SJOSão Carlos/SCAItalianos/ITASanta Luzia/SLUSanto Agostinho/SATBrunhara/BRULaudo Natel/LANSant’Anna/SAA

Lindóia (SP) São Benedito/SBE YesBioleve/BIO Yes

Termas deIbirá (SP)

Jorrante/JOR Paraná Porous andFractures

Sandstones Bauru Gp. (Cretaceous)Ademar de Barros/ADB Basalts Serra Geral Fm.

(Jurassic-Cretaceous)Carlos Gomes/CGOSaracura/SRCSeixas/SEI

Águas de SantaBárbara (SP)

Balneário Paraná Porous andFractures

Sandstones Bauru Gp. (Cretaceous)Municipal/BMU Basalts Serra Geral Fm.

(Jurassic-Cretaceous)Lambari (MG) No. 1/LA1 Southeastern

shieldPorous andfractures

Ortogneisses Paraíba do Sul Gp.(Proterozoic)

No. 2/LA2 Granulites Barbacena Gp.(Proterozoic)

No. 3/LA3 Migmatites São João dél Rei Gp.(Proterozoic)

No. 4/LA4 Metassedimentaryseq.

Andrelândia Gp.(Proterozoic)

No. 5/LA5 Metavulcanossedimentaryseq.

magmatic plutonicseries (Brasiliano)

No. 6/LA6São Lourenço

(MG)No. 7-Bis/SL7No. 5-Alcalina/SL5No. 6-Sulfurosa/SL6No. 3-Vichy/SL3No. 4-Ferruginosa/SL4No. 1-Oriente/SL1No. 10-Primavera/SL10No. 9-Carbogasosa/SL9

Cambuquira(MG)

Roxo Rodrigues/RORRegina Werneck/REWCom. AugustoFerreira/CAFFernandes Pinheiro/FEPMarimbeiro/MARSouza Lima/SLI

Caxambu(MG)

Geiser Florianode Lemos/GFLVenâncio/VENMayrink/MAY

(continued on next page)

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e30 23

Table 1 (continued )

City (Statea) Spring (well)name/Sample code

HydrogeologicalProvinceb

Dominant flow Major rock types Geological context/age Commercializationc

Ernestina Guedes/EGUViotti/VIOD. Pedro II/DPEBeleza/BZADuque de Saxe/DXEDa. Leopoldina/LEODa. Isabel/Conde dÉu/ISA

Poços deCaldas (MG)

Quisisana/QUI Southeasternshield

Fractures Alkaline rocks Poços de Caldasintrusive complex

XV de Novembro/NOV Nepheline syenites (Cretaceous)Macacos/MAC PhonolitesSinhazinha/SIN PyroclasticsFrayha/FRA Volcanic tuffsPedro Botelho/PEB

Pocinhos doRio Verde (MG)

Rio Verde/RIVSamaritana/SMASão José/SJOAmorosa/AMO

Araxá (MG) Dona Beja/DBJ Southeasternshield

Porous andfractures

Quartzites and schists CretaceousAndrade Júnior/AJU Alkaline-carbonatitic rocks PreCambrian

a SP ¼ São Paulo, MG ¼ Minas Gerais.b According to Mente (2008).c Water commercialized by private company in addition to consumption in taps accessible to population in public areas.

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e3024

dykes or alkaline breccias (Caxambu) (CPRM, 1999). The local con-ditions favor the periodical eruption (up to 5-m height) of a non-geothermal geyser at the Caxambu waterpark due to the build-upof pressure from dissolved carbon dioxide in the water.

Araxá city is geologically located at Alto Paranaíba IgneousProvince that includes the renowned carbonatite intrusion ofAraxá, which covers approximately 16 km2 and is in general relatedto a NW-trending linear structure bordering the São Franciscocratonic area that is thought to be in evidence since late Precam-brian times (Traversa et al., 2001). Two springs were sampled atAraxá city: 1) Dona Beja, associated to an aquifer system classifiedas granular, free and semi-confined, mainly in the intrusive bodydomain (Beato et al., 2000); 2) Andrade Júnior, related to a deepfractured aquifer, unconfined to semi-confined, mainly occurring inrocks surrounding the carbonatite complex (Beato et al., 2000).

3. Sampling and analytical methods

The sampling points (75) were chosen according to the hydro-chemical information from previous studies and to the easy accessfor collection. The groundwater chemical composition is attaineddue to processes occurring at the liquidesolid interface whendifferent rock matrices are extensively leached.

The sampling sites were (Fig. 1 and Table 1): Águas de São Pedro(3water sources), Águas da Prata (7 water sources), Águas de Lindóia(7 water sources), Serra Negra (8 water sources), Lindóia (2 watersources), Termas de Ibirá (5 water sources), Águas de Santa Bárbara(1 water source), Lambari (6 water sources), São Lourenço (8 watersources), Cambuquira (6 water sources), Caxambu (10 water sour-ces), Poços de Caldas (6 water sources), Pocinhos do Rio Verde (4water sources) and Araxá (2 water sources). All water sources(except geyser “Floriano de Lemos”, Caxambu city) have been usedfor drinking purposes in thermal and non-thermal spas and some ofthem are commercialized by private companies (Table 1).

The sampling campaign occurred betweenMarch and June 2012(autumn), when the local air temperaturewas often lower than thatof the summer months (average in January ¼ 30e32 �C). Therainfall was lower than that of the wet season (summer,DecembereJanuary) but higher than that of the dry season (winter,JulyeAugust).

About 500 mL of groundwater sample was directly taken fromtaps/pipes installed in each spring/well, which was stored in glass/plastic flasks of variable volume as required by each gas (222Rn,220Rn, O2, CO2 and H2S) analysis. Temperature was also measuredby the use of a digital portable meter in addition to the dissolvedgases readings. All data acquisition was in situ performed foravoiding gases losses and modification of other physical andchemical parameters of the waters.

The dissolved oxygen (DO) concentration was determined in adigital portablemeter recording the potential values generated by anO2 sensible electrode consisting on a metallic wire covered by a thingold layer (detection limit ¼ 0.1 mg/L). The electrode was insertedinto a 60-mL Winkler bottle filled with the water sample, then, thefinal valuewas recorded after stabilization of the reading. All DOdatawere corrected due to differences in altitude of the sampling points,using as reference the value corresponding to the sea level.

The carbon dioxide was evaluated by the buret titration methodon using water volumes of 25 or 50 mL (Hach, 1992). This amountwas inserted in a clean erlenmeyer flask, then, one powder pillowof a phenolphthalein indicator solution (5 g/L) (Hach, 1992) wasadded and the solution mixed gently. A 25-mL buret was filled tothe zero mark with 0.0227 N NaOH solution and the preparedsamplewas titrated while gently swirling the flask until a light pinkcolor formed and persisted for 30 s. The reaction of NaOH with CO2(as carbonic acid) occurs in two steps, first a reaction from carbonicacid to bicarbonate and then to carbonate. Because the conversionof CO2 to bicarbonate is complete at pH 8.3, phenolphthalein wasused as a color indicator for the titration (Hach,1992). The dissolvedCO2 (in mg/L) was calculated on multiplying the volume (in mL) ofthe titrant used by the factor 20 (sample volume¼ 50mL; detectionlimit ¼ 2 mg/L) or 40 (sample volume ¼ 25 mL; detectionlimit ¼ 4 mg/L) (Hach, 1992). The pink color in some samples wasimmediately formed with the addition of the phenolphthalein in-dicator. The dissolved CO2 corresponded to 0 mg/L in these cases asit was not necessary the addition of the titrant (0.0227 N NaOHsolution) for the color change.

The dissolved sulfide gas was determined by colorimetry(wavelength 665 nm) using a program stored in the Hach DR/2000spectrophotometer (Hach, 1992). The methylene blue method wasadopted in which the hydrogen sulfide and acid-soluble metal

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e30 25

sulfides react with N,N-dimethyl-p-phenylenediamine oxalate toform methylene blue (Hach, 1992). One glass cell (the preparedsample) was filled with 25 mL of sample, whereas another (theblank) was filled with 25 mL of deionized water. Then, 1 mL ofSulfide 1 Reagent (N,N-dimethyl-p-phenylenediamine oxalate) wasadded to each cell and, after mixing, 1 mL of Sulfide 2 Reagent(potassium dichromate) was put into both cells. After mixing and a5-minute reaction time, the blank was inserted into the cell holder,the spectrophotometer was set to zero reading, the preparedsample was placed into the cell holder and the equipment dis-played the result in mg/L sulfide (S2�) (Hach, 1992). The intensity ofthe blue color was proportional to the sulfide concentration andproper dilution was used to determine high sulfide levels is somesamples. The detection limit of the method corresponded to 1 mg/Lsulfide.

The radon and thoron dissolved in water were analyzed on siteusing RAD7 alpha particles detector coupled to accessory RADH2Ofrom Durridge Co. The RAD7 utilizes a solid state alpha detector,comprising a Si semiconductor material that converts the energy ofthe alpha particles into an electrical signal. The accumulation ofmany signals results in a spectrum that is presented on a scale ofalpha energy in the range of 0e10 MeV. Such energy interval issuitable for 222Rn and 220Rn readings as data acquisition takes placebetween 6 and 9 MeV (Durridge, 2009a). The spectrum is displayedin a set of 200 channels grouped into eight windows of differentenergy range. A, B, C and D are the main windows, whereas E, F, Gand H are the diagnostic of main windows. Windows A and Cprovide 222Rn activity concentration data from 218Po and 214Podecays, representing “new” (218Po) and “old” (214Po) 222Rn,respectively (Durridge, 2009a). Windows B and D provide 220Rnactivity concentration data from 216Po and 212Po decays, repre-senting “new” (216Po) and “old” (212Po) 220Rn, respectively(Durridge, 2009a). Thus, the RAD7 separates the radon and thoronsignals by energy of the alpha particles from their progeny,becoming possible to measure both Rn isotopes simultaneously(Durridge, 2009a). The equipment was factory calibrated by way ofinter-comparison with radon chambers run by the U.S. EPA and theU.S. Department of Energy (Durridge, 2009a).

The groundwater samples were collected in 100-mL flasks,avoiding as much as possible the exposure to atmospheric air. TheRADH2O accessory unit employed an aeration system in a closedcircuit connecting the sample, RAD7 and a desiccant tube con-taining Drierite to humidity absorption (Durridge, 2009b). Then,the air circulated through the sample during about 10 min,extracting radon and thoron until reaching an equilibrium state (forreadings in windows A and B). The radon and thoron extractedwere pumped into the RAD7, where their progeny were detected.The instrument display recorded the dissolved 222Rn and 220Rnactivity concentration data in pCi/L that were converted to the SIunit (Bq/L for 222Rn and mBq/L for 220Rn). The Detection Limit (DL)corresponded to 4 mBq/L (Durridge, 2009a), whereas the un-certainties given of the results were one standard deviations,resulting from propagation of all statistical uncertainties in theentire measurement process. The low activity concentration insome samples implied on high analytical uncertainty as reportedelsewhere (for instance, Jia et al., 2002).

4. Results and discussion

4.1. Temperature and dissolved oxygen, carbon dioxide and sulfidein the waters

The groundwater temperature ranged from 20.4 to 35.7 �C(mean ¼ 24.8 �C) (Table 2). According to the BCMW guidelines fortemperature (DFPM, 1966), three categories can be defined for the

analyzed waters: cold (values lower than 25 �C ¼ 41 samples),hypothermal (values ranging from 25 to 33 �C ¼ 33 samples) andmesothermal (values ranging from 33 to 36 �C ¼ 1 sample).

The mean dissolved oxygen (DO) concentration was 3.5 mg/L(Table 2). The lowest DO content was 0.8 mg/L (Macacos spring,Poços de Caldas city, Minas Gerais State), whereas the highest DOconcentration was 9 mg/L (São Benedito water source, Lindóia city,São Paulo State) that corresponds to the solubility of oxygen at 100%air saturation at 21 �C and 760 mmHg mount air barometric pres-sure (EIFAC, 1986). The gas content (in solution) of a mass of watercan be evaluated considering the Henry’s law and Dalton’s law ofpartial pressure. From both gas laws, it has been widely recognizedthat the solubility of oxygen in water varies with temperature, theDO content reducing sharply with increase in temperature (Cole,1983; APHA, 1985; EIFAC, 1986). Treusdale et al. (1955) reportedthe solubility value for oxygen at various temperature, which wasre-estimated using improved Henry coefficients (Benson andKrause, 1980) as discussed by Cole (1983). The values of solubilityof oxygen in water at various temperatures, from moist air at760mmHg at 0.0 ppt salinity, taken from EIFAC (1986) is 9.1 mg/L at21 �C and 6.9 mg/L at 35 �C. There is a significant inverse rela-tionship between temperature and dissolved O2 in the analyzedgroundwater (Fig. 2a), confirming that the increase in temperaturecauses a decrease in dissolved O2. The two-tailed P value estimatedby GraphPad software from the Pearson correlation coefficient(r ¼ �0.41, n ¼ 75; Fig. 2a) equals 0.0003 by conventional criteria,suggesting this difference is extremely statistically significant.

The mean dissolved CO2 concentration was 590 mg/L (Table 2).The dissolved CO2 was absent in nine samples, from which fivewere collected at Termas de Ibirá city in São Paulo State. Degassingfavored by cracks, faults and fissures in basalts of the Serra GeralFormation may be a possible reason for the null CO2 values atTermas de Ibirá city. The dissolved CO2 ranged from 52 to 1840 mg/L in the remaining samples (Table 2) and its presence in waters ismainly related to the carbonates dissolution in the rock matrices.The groundwater temperature range is from 25 to 35.7 �C in thehypothermal and mesothermal waters (Table 2) and such largedifference (10.7 �C) favors the significant inverse relationship be-tween temperature and dissolved carbon dioxide (Fig. 2b), indi-cating that its solubility decreases accompanying the temperatureraising as also verified for oxygen. The two-tailed P value estimatedby GraphPad software from the Pearson correlation coefficient(r ¼ �0.49, n ¼ 34; Fig. 2b) equals 0.0033 by conventional criteria,suggesting this difference is very statistically significant.

According to the BCMW guidelines, the carbogaseous waterscontain dissolved carbon dioxide gas corresponding to a minimumof 200 mL per liter of water (DFPM, 1966). The CO2 concentrationdata in Table 2 can be used for estimating the CO2 volume (in mL)per liter of water from the ideal gas law that is the state equation ofa hypothetical (ideal) gas. Although it has limitations, it is a roughapproximation to the behavior of some gases like CO2, under someconditions. It is often written as PV ¼ nRT where P is the gaspressure, V is the gas volume, n is the gas number of moles, T is thegas temperature and R is the ideal, or universal, gas constant. If T isexpressed in Kelvin, then, R ¼ 0.0821 L.atm/K.mol. Rememberingthat 1 mol CO2 corresponds to approximatelly 44 g, then, it ispossible estimate V values (in mL) varying from 0 to 1025 mL(Table 2).

The comparison of the V values (in mL) for CO2 in Table 2 withthe BCMW guideline of 200 mL per liter of water (DFPM, 1966)indicates that 33water sources are carbogaseous. However, some ofthem are popularly recognized by other chemical attributes ratherthan dissolved CO2, for instance: No. 2 (Lambari city) and No. 5 (SãoLourenço city) are said alkaline waters; No. 3 (Lambari city) andCom. Augusto Ferreira (Cambuquira city) are said magnesian

Table 2Temperature, dissolved gases, radon and thoron data in groundwater samples analyzed in this paper.

Sample codea Temp. (�C) O2 (mg/L) CO2 (mg/L) CO2 (mL)b H2S (mg/L) 222Rn (Bq/L)c 220Rn (mBq/L)c 222Rn ( � 10�5 J/yr)d 220Rn ( � 10�5 J/yr)d

ALS 27.1 3.13 120 67.2 0.003 1.4 � 0.2 52 � 63 0.55 0.29GIO 27.4 5.08 100 56.1 0.006 1.7 � 0.2 <4 0.68 <0.02JUV 26.7 2.81 88 49.2 3.064 0.02 � 0.02 <4 0.01 <0.02PLA 25.4 1.33 400 222.8 0.005 24.4 � 1.2 270 � 185 9.91 1.50POL 25.8 3.06 800 446.2 0.012 4.8 � 0.5 200 � 144 1.95 1.11VIT 24.5 1.33 1032 573.2 0.002 53.3 � 1.8 63 � 81 21.60 0.35BOI 24.2 3.77 128 71.0 0.004 74.7 � 2.2 52 � 63 30.30 0.29PTA 25.1 7.14 180 100.2 0.004 23.2 � 1.2 70 � 74 9.43 0.39VIL 24.3 5.71 140 77.7 0.003 104.3 � 3.3 226 � 185 42.30 1.25PDE 23.7 5.10 256 141.8 0.004 5.6 � 0.6 255 � 148 2.28 1.42SIL 22.5 5.35 96 53.0 0.001 22.1 � 1.1 15 � 22 8.96 0.08FIL 26.9 4.65 108 60.5 0.002 7.8 � 0.6 200 � 137 3.17 1.11BEL 26.4 3.84 88 49.2 0.002 8.3 � 0.7 67 � 70 3.36 0.37SRE 27.3 4.44 164 91.4 0.002 5.0 � 0.5 <4 2.01 <0.02COM 23.6 6.06 100 55.4 0.001 6.0 � 0.6 15 � 22 2.42 0.08LIN 24.6 5.66 136 75.6 0.004 7.4 � 0.6 226 � 144 2.99 1.25CUR 26.2 4.65 128 71.5 0.005 9.2 � 0.7 89 � 85 3.74 0.49SJO 22.0 6.16 132 72.7 0.002 10.0 � 0.7 7 � 11 4.04 0.04SCA 21.7 5.66 236 129.8 <0.001 10.8 � 0.7 15 � 22 4.37 0.08ITA 20.4 5.66 212 116.1 0.008 5.8 � 0.6 26 � 37 2.36 0.14SLU 21.5 2.83 188 103.4 0.001 25.0 � 1.2 181 � 133 10.15 1.01SAT 21.8 3.23 236 129.9 0.002 31.4 � 1.4 240 � 148 12.74 1.33BRU 22.1 4.85 160 88.1 0.001 30.2 � 1.3 418 � 222 12.24 2.32LAN 23.1 3.64 212 117.2 0.003 6.2 � 0.6 15 � 26 2.51 0.008SAA 21.9 4.65 200 110.1 0.001 23.9 � 1.1 26 � 37 9.72 0.14SBE 24.9 9.05 180 100.1 0.003 10.3 � 0.7 56 � 63 4.17 0.31BIO 23.6 6.45 132 73.1 0.003 2.4 � 0.4 <4 0.98 <0.02JOR 26.8 2.05 0 0 0.013 0.5 � 0.1 <4 0.20 <0.02ADB 27.2 2.59 0 0 0.003 2.7 � 0.4 26 � 41 1.10 0.14CGO 28.4 1.30 0 0 0.005 3.4 � 0.4 26 � 33 1.36 0.14SRC 28.7 0.97 0 0 0.035 3.6 � 0.4 26 � 41 1.46 0.14SEI 26.4 2.38 0 0 0.008 2.4 � 0.3 <4 0.97 <0.02BMU 24.6 5.99 252 140 0.002 1.3 � 0.2 26 � 37 0.54 0.14LA1 23.0 5.00 1840 1016.8 0.001 8.2 � 0.6 78 � 81 3.32 0.43LA2 23.0 4.69 1600 884.1 0.002 10.3 � 0.7 259 � 148 4.19 1.44LA3 23.1 4.49 1480 818.1 0.001 13.5 � 0.8 237 � 148 5.48 1.31LA4 24.0 4.69 600 332.7 <0.001 9.6 � 0.7 81 � 81 3.89 0.45LA5 25.4 6.73 1840 1025.0 <0.001 7.9 � 0.6 26 � 37 3.20 0.14LA6 24.0 5.51 1480 820.6 <0.001 8.5 � 0.7 44 � 56 3.44 0.25SL7 24.7 1.53 800 444.6 0.018 1.6 � 0.3 22 � 30 0.67 0.12SL5 23.6 1.73 1560 863.8 <0.001 1.1 � 0.2 48 � 56 0.44 0.27SL6 25.2 1.22 1720 957.5 <0.001 4.1 � 0.4 41 � 52 1.68 0.22SL3 26.7 3.67 1320 738.5 <0.001 4.4 � 0.5 78 � 78 1.80 0.43SL4 26.6 1.94 920 514.6 <0.001 4.0 � 0.4 33 � 44 1.64 0.18SL1 25.6 1.33 1420 791.6 <0.001 0.9 � 0.2 33 � 44 0.37 0.18SL10 25.2 3.06 1200 668.0 <0.001 4.8 � 0.6 41 � 52 1.95 0.22SL9 23.9 1.02 1480 820.3 <0.001 3.6 � 0.4 52 � 59 1.44 0.29ROR 24.0 3.74 800 443.6 0.001 1.5 � 0.3 92 � 92 0.62 0.51REW 24.0 3.03 1380 765.1 0.003 4.6 � 0.5 333 � 185 1.85 1.85CAF 26.3 4.34 1000 558.7 0.001 3.0 � 0.4 100 � 89 1.21 0.55FEP 25.0 2.63 1760 979.1 0.040 13.4 � 0.9 67 � 74 5.42 0.37MAR 25.5 3.33 1200 668.7 0.004 1.6 � 0.3 218 � 148 0.66 1.21SLI 23.2 3.13 1080 597.2 0.013 0.8 � 0.2 <4 0.32 <0.02GFL 23.8 4.69 1100 609.5 0.014 3.0 � 0.4 895 � 333 1.21 4.97VEN 25.0 2.86 1680 934.6 0.017 4.8 � 0.6 314 � 222 1.94 1.74MAY 25.5 4.18 800 445.8 0.004 35.3 � 1.5 444 � 259 14.34 2.46EGU 25.8 1.73 1600 892.5 <0.001 10.1 � 0.8 492 � 222 4.08 2.73VIO 25.3 1.84 800 445.5 0.015 45.9 � 1.8 418 � 259 18.62 2.32DPE 24.7 1.94 880 489.1 0.009 40.7 � 1.8 63 � 74 16.52 0.35BZA 23.9 1.84 1440 798.1 0.001 6.9 � 0.7 385 � 222 2.79 2.13DXE 25.4 1.84 720 401.1 0.007 8.0 � 0.7 192 � 144 3.23 1.07LEO 24.5 1.02 680 377.7 0.047 18.4 � 1.1 81 � 85 7.48 0.45ISA 24.2 1.53 920 510.4 0.010 5.3 � 0.6 148 � 122 2.15 0.82QUI 22.4 2.25 104 57.4 0.001 8.4 � 0.7 52 � 67 3.41 0.29NOV 25.7 1.37 0 0 0.259 16.2 � 0.9 96 � 89 6.58 0.53MAC 32.1 0.78 0 0 1.184 2.0 � 0.3 <4 0.82 <0.02SIN 25.7 2.94 140 78.1 0.003 35.5 � 1.4 522 � 259 14.40 2.89FRA 23.2 3.82 52 28.8 <0.001 23.2 � 1.2 866 � 296 9.40 4.80PEB 35.7 1.18 0 0 0.383 17.6 � 1.0 292 � 185 7.15 1.62RIV 23.3 1.30 180 99.6 0.756 36.3 � 1.5 81 � 85 14.75 0.45SMA 23.9 1.40 80 44.3 0.522 10.4 � 0.8 178 � 141 4.20 0.98SJO 22.0 1.30 60 33.0 0.528 41.1 � 1.5 89 � 89 16.67 0.49AMO 21.7 5.80 112 61.6 0.004 31.4 � 1.4 15 � 26 12.73 0.08DBJ 22.1 5.00 252 138.8 0.001 112.5 � 3.0 141 � 133 45.65 0.78

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e3026

Table 2 (continued )

Sample codea Temp. (�C) O2 (mg/L) CO2 (mg/L) CO2 (mL)b H2S (mg/L) 222Rn (Bq/L)c 220Rn (mBq/L)c 222Rn ( � 10�5 J/yr)d 220Rn ( � 10�5 J/yr)d

AJU 29.0 1.60 0 0 1.980 7.0 � 0.6 26 � 37 2.82 0.14Min. 20.4 0.78 0 0 <0.001 0.02 <4Max. 35.7 9.05 1840 1025 3.064 112.5 895Mean 24.8 3.46 590 328 0.121 15.4 141SDe 2.4 1.83 597 332 0.447 20.9 178

a For sample description, see Table 1.b Volume of dissolved CO2 per liter of water.c Analytical uncertainty corresponding to 1s standard deviation.d Annual potential a-energy intake (UNSCEAR, 2006).e SD ¼ Standard Deviation.

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e30 27

waters; No. 5 (Lambari city), No. 4 (São Lourenço city) and Fer-nandes Pinheiro (Cambuquira city) are said ferruginous waters; No.6 and No. 7 Bis (São Lourenço city) and Souza Lima (Cambuquiracity) are said sulfured waters.

Carbogaseous springs exhibiting free CO2 content over 250mg/Lhave been recognized elsewhere, for instance, Daylesford(Australia), Bad Gleichenburg (Austria), Vichy (France), Bad Ems(Germany), Bath (England), Balatonfüred (Hungary), Hvergerdi(Iceland), Chianciano Terme (Italy), Narugo (Japan), Yura (Peru),Pedras Salgadas (Portugal), Pyatigorsk (Russia), Rogaska (Slovenia),Rheinfelden (Switzerland) and Saratoga Springs (USA) (Altman,2000). In Spain, a study was held by Eyzaguirre (2003) thatinvolved 12 field trips summing up to 15,056 km and encompassedanalytical determinations for 95 Spanish mineral-medicinal watersfrom 82 balnearies. Carbogaseous waters were recognized for only8 water sources, which possessed CO2 contents between 253 mg/L(Mondariz-Gándara, Pontevedra) and 742.5 mg/L (Laranjón-Capilla,Granada) (Eyzaguirre, 2003). Table 2 shows that 29 groundwatersamples analyzed in this paper contain dissolved CO2 higher than742.5 mg/L that is the maximum value found by Eyzaguirre (2003).

The dissolved H2S concentration was below the detection limitof the spectrophotometric method (1 mg/L) in 13 groundwatersamples (Table 2). The remaining water sources contained between0.001 and 3.06 mg/L of dissolved sulfide. Contrarily to O2 and CO2,no significant relationship was found between temperature anddissolved sulfide in the analyzed waters. According to the BCMWguidelines, the sulfured waters contain dissolved sulfur corre-sponding to aminimumof 0.001 g per liter (¼1mg/L) (DFPM,1966).This only happened for the following waters (Table 2): Juventude(Águas de São Pedro city), Macacos (Poços de Caldas city) andAndrade Júnior (Araxá city). However, other water sources havebeen also popularly named as sulfured despite they do not strictlyadhere to the BCMWguideline of 1 mg/L, i.e.: Rio Verde (0.76mg/L),Samaritana (0.52 mg/L) and São José (0.53 mg/L) at Pocinhos do RioVerde city; XV de Novembro (0.26 mg/L) at Poços de Caldas city;Souza Lima (0.01 mg/L) at Cambuquira city; No. 6 (<0.001 mg/L)and No. 7 Bis (0.018 mg/L) at São Lourenço city. In Spain, sulfuredwaters were recognized by Eyzaguirre (2003) in 21 water sources,which possessed H2S contents between 1.3 mg/L (Laias, Orense)and 36.8 mg/L (Fuente Amarga, Cádiz), most of themwell above themaximum value found in this paper (3 mg/L).

4.2. Dissolved radon and thoron in the waters

The 222Rn activity concentration ranged from 0.02 to 112.5 Bq/L,whereas the 220Rn activity concentration range was <4e895 mBq/L) (Table 2).

Numerous papers are available on the determination of radon inmineral waters, some of them pointing to the use of treatmentsinvolving the intake of radon gas through inhalation or by trans-cutaneous resorption of radon dissolved in water. For instance,natural and artificial grottoes carved in the rock bathing tubs found

in some of the oldest spas in Central and Southern Europe havebeen considered by Zdrojewicz and Strzelczyk (2006) who reportedhigh 222Rn levels of 2000e4000 Bq/L at the island of Ischia in thevolcanic area near Naples, Merano and Lurisia spas in the alpineregion (Italy). In Spain, radioactive waters (222Rn activity concen-tration higher than 67.3 Bq/L) were recognized by Eyzaguirre(2003) in 24 water sources that exhibited 222Rn levels between73 Bq/L (Caldas de Boí-Tartera, Lérida) and 1868 Bq/L (Arnedillo, LaRioja). In this paper, the highest 222Rn levels (75e112 Bq/L) werefound in Boi and Villela springs located at Águas da Prata city (SãoPaulo State) and Dona Beja spring situated at Araxá city (MinasGerais State) that are well below of many values reported byEyzaguirre (2003) and Zdrojewicz and Strzelczyk (2006).

In contrast to the abundant reports focusing 222Rn in mineralwaters, only a few studies have been done on the quantitativedetermination of thoron, because of the difficulties in measuringthe radioactivity of a gaseous isotope with a half life of w56 s.Among the exceptions is the investigation held by Misdaq andChaouqi (2008) who measured the 220Rn activity concentration in13 bottled mineral water samples from Morocco, France, and Italywidely consumed by the European population living in Marrakechcity (Morocco). Misdaq and Chaouqi (2008) reported 220Rn levelsranging from 0.91 to 3.4 Bq/L that are above of the values found inthis paper (<0.004e0.9 Bq/L; Table 2).

Thus, in this paper, the highest 222Rn levels were found insprings situated at Águas da Prata city (São Paulo State) and Araxácity (Minas Gerais State). Águas da Prata city is placed in the borderof the Poços de Caldas alkaline complex that is awell-knownmassifcharacterized by the presence of high natural radioactivity(Bonotto, 2010). It comprises a suite of alkaline volcanic andplutonic rocks (mainly phonolites and nepheline syenites) whichaccumulate the natural radioelements uranium and thorium andrare-earth elements (REEs) (Schorscher and Shea, 1992). In Araxácity, Dona Beja spring is located at the Barreiro area, where uraniumcan occur widely disseminated in the pyrochlore matrix as a traceconstituent (100 ppm U3O8) or may characterize an uraniferouspyrochlore with the U3O8 concentration reaching up to 2% (Castroand Souza, 1970). U3O8 contents varying between 150 and200 ppm have also been reported in the large phosphate deposit atBarreiro area, which has been extensively explored by Bunge (pastSerrana). Uranium also occurs associated to the REEs at the central-northern portion of Barreiro area. The genesis of this deposit islinked to the presence of the REEs-enriched carbonatite thatformed a closed ellipsoidal structure (Grossi Sad and Torres, 1976).

WHO (2011) proposed that controls should be implemented ifthe 222Rn concentration of drinking-water for public water suppliesexceeds 100 Bq/L, i.e. treatment of the water source should beundertaken to reduce the 222Rn levels to well below 100 Bq/L. Acomparison of this value with the results reported here indicatesthat it was exceeded in Villela spring (104.3 Bq/L) and Dona Bejaspring (112.5 Bq/L) (Table 2). Both water sources are not utilized inwater-supply systems but are available for ingestion by population

Fig. 2. Diagrams showing the relationship between (a) temperature and dissolvedoxygen of all analyzed waters and (b) temperature and carbon dioxide of the hypo-thermal and mesothermal waters.

Fig. 3. The relationship between dissolved thoron (220Rn, in mBq/L) and radon (222Rn,in Bq/L) in the hypothermal and mesothermal waters analyzed in this paper.

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e3028

in public areas. Despite they are just occasionally ingested, it isimportant emphasize that some caution would be needed for theirconsumption due to the high 222Rn levels.

There is a significant direct relationship between dissolvedradon and thoron in the hypothermal and mesothermal waters(Fig. 3). The two-tailed P value estimated by GraphPad softwarefrom the Pearson correlation coefficient (r ¼ 0.72, n ¼ 34; Fig. 3)equals 0.0001 by conventional criteria, suggesting this difference isextremely statistically significant. Such finding is perhaps related totemperature effects on the dissolution of their parents 226Ra and224Ra from the rock surfaces. 222Rn and 220Rn would be producedthrough a-decay of 226Ra and 224Ra, respectively, after their releaseinto the liquid phase. The dissolution processes would be favoredduring the interactions involving the higher temperature watersand the grain boundaries and/or multi-grain aggregates in rocksand minerals. This is because they possess temperature values thatare above up to about 11 �C of the lowest ones.

According to the BCMW guidelines (DFPM, 1966), the thorif-erous waters contain dissolved thoron corresponding to a mini-mum of 2 Mache units per liter. The equivalence that 1 Mache unitper liter corresponds to 275 pCi/L (¼10.2 Bq/L) (UNSCEAR, 2006)may be applied to the data set given in Table 2. Thus, it is possibleobtain 220Rn activity concentration varying between <0.0004 and0.088Mache unit/L, which is a rangewell below the reference valueof 2 Mache unit/L. Therefore, none of the waters analyzed arethoriferous, despite people involved in the marketing andcommercialization of some waters usually consider them possess-ing significant levels of dissolved thoron.

According to the BCMW guidelines (DFPM, 1966), the radioac-tive waters contain dissolved radon according to three differentlevels of Mache units: weakly radioactive (radon content between 5and 10 Mache units per liter), radioactive (radon content between

10 and 50 Mache units per liter) and strongly radioactive (radoncontent higher than 50 Mache units per liter). Thus, values below 5Mache unit per liter indicate the waters are non-radioactive. Theconversion of the 222Rn activity concentration data given in Table 2to Mache units yields a classification of non-radioactive for prac-tically all waters, as the values often varies between 0.003 and4.51 Mache unit/L. The unique exceptions are Vitória (5.24 Macheunit/L), Boi (7.34 Mache unit/L), Villela (10.25 Mache unit/L) andDona Beja (11.05 Mache unit/L) springs.

Therefore, according to the BCMW guidelines (DFPM, 1966), thewaters of Vitória and Boi springs are weakly radioactive (radon con-tent within the range of 5e10 Mache units per liter), whereas thewaters of Villela andDona Beja springs are radioactive (radon contentwithin the range of 10e50 Mache units per liter). Such findingscontradict the “common sense” classification of radioactive forseveral water sources studied here like: Balneário Municipal (Águasde Santa Bárbara city); São Carlos and Italianos (Serra Negra city); RioVerde, Samaritana and São José (PocinhosdoRioVerde city);Mayrinkand Viotti (Caxambu city). The data reported in Table 2 clearly in-dicates that thesewaters arenon-radioactive in termsof thedissolvedradon guideline established by the BCMW (DFPM, 1966).

4.3. Radiation dose due to 222Rn and 220Rn

222Rn has been recognised, along with its decay products, to bethe most important source of exposure to natural radioactivity.Consequently, widespread and intensive work has been conductedon monitoring activity, research into fundamental release andtransport mechanisms, development and improvement of mea-surement techniques, research on remedial actions, etc. The case ofthoron (220Rn) is very different from that of radon as due to its shorthalf-life, the activity concentration generally does not reach a highenough value for its decay products to produce significant doses.The low health interest in 220Rn, further evidenced by the lack ofattention in some ICRP publications (for instance, ICRP, 1987, 1991)along with experimental difficulties in conducting in-field mea-surements, have, over time, increased the gap between knowledgeabout radon and thoron. Nevertheless, in certain situations, thoronexposure can produce a dose comparable to that from radon.

The adoption of some dose conversion factor (DCF) (IAEA, 1996;WHO, 2011) is required to estimate committed effective doses due

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e30 29

to the radionuclides in waters. However, there is no consensus inthe literature on the DCF value for 222Rn and 220Rn. A value of10�8 Sv/Bq resulting from the application of a modified ICRP modelfor the 222Rn ingestion in water has been sometimes adopted(Kendall et al., 1988; Oliveira et al., 2001; Bonotto, 2004). Bonotto(2011) utilized DCF ¼ 1.4 � 10�6 mSv/Bq when studying the ma-jor aquifer systems of the Paraná sedimentary basin, Brazil, whichwas estimated considering the individual dose criterion of 0.1 mSv/year (WHO, 2011) and the guideline 222Rn volumetric activity valuein drinking water of 100 Bq/L for public water supplies (WHO,2011).

Despite several papers have been published on dosimetricmodels for radon decay products, very few dosimetric studies dealwith thoron decay products. Some available dose conversion fac-tors for them have been expressed as the effective dose (in Sv) perunit of exposure (in J h m�3). They were generally based on olddosimetric models and on outdated values for aerosol and physi-ological parameters (Nuccetelli and Bochicchio, 1998). OECD/NEA(1983) assumed DCF ¼ 0.52 Sv per J h m�3 for adults exposed to220Rn indoors, whereas for children the value was estimated to beup to twice as high. UNSCEAR (1993) reportedDCF ¼ 0.42 Sv per J h m�3, referring to all organs and tissue andassuming an indoor occupancy factor of 100%, while the valuecalculated for the lung and for an indoor occupancy factor of 80%would be 0.35 Sv per J h m�3. IAEA (1996) assumedDCF ¼ 0.48 Sv per J h m�3 that would be valid only for workers,whereas CEU (1996) expressed DCF ¼ 0.5 Sv per J h m�3 forexposure in workplaces that was called “conventional”.

Radon and thoron decay product exposure rates have been alsospecified by the measure of potential alpha energy concentration(PAEC), given in units of J m�3 and the equilibrium-equivalentconcentration (EEC), expressed in Bq m�3. The PAEC is derivedfrom a linear combination of the activities of the short-lived decayproducts in each 222Rn and 220Rn series (UNSCEAR, 2000). Theconstants in the linear combination are the fractional contributionsof each decay product to the total potential alpha energy(UNSCEAR, 2000). The EEC (in Bq m�3) can be converted to thePAEC by the relationships (UNSCEAR, 2006):1 Bqm�3¼ 5.56� 10�9 J m�3 for 222Rn; 1 Bqm�3¼ 7.6� 10�8 J m�3

for 220Rn.IAEA (1996) expressed the limits on intake for radon and thoron

progenies. The maximum in a single year of the potential a-energyintake for radon progeny corresponds to 0.042 J, whereas for thoronprogeny is 0.127 J. Such guideline values are useful to perform adosimetric evaluation from 222Rn and 220Rn activity concentrationdata. The values in Bq/L (Table 2) are converted into Bq/m3

(1m3¼103 L), fromwhich it is possible estimate the PAEC (in J m�3)for radon and thoron. WHO (2011) established guidance levels forseveral radionuclides in drinking water, assuming that 730 L is theannual ingested volume of water (equivalent to 2 L per day). Themultiplication of such amount (0.73 m3) by the PAEC for radon andthoron yields the annual potential a-energy intake (in J yr�1) for222Rn and 220Rn progenies (Table 2).

The maximum a-energy intake for radon progeny correspondedto 0.4 � 10�3 J as reported in Table 2 for Villela and Dona Bejasprings. It is about 100 times lower than the guideline value of0.042 J reported by IAEA (1996). These water sources also exhibitedthe highest 222Rn activity concentration, i.e. exceeded the WHO(2011) guideline value of 100 Bq/L. The maximum thoron progenyintake was 5 � 10�5 J for the geyser at Caxambu city, Minas GeraisState (Table 2). It is almost 2600 times lower than the IAEA (1996)guideline value of 0.127 J and circa 80 times lower than themaximum a-energy intake for radon progeny at Villela and DonaBeja springs. Thus, 220Rn doses are much lower than that of 222Rnwhat is compatible with the widespread and intensive work

conducted on monitoring radon elsewhere as the thoron activityconcentration generally does not reach a high enough value for itsdecay products to produce significant doses.

Another significant finding is the congruency between thehighest 222Rn and 220Rn activity concentration and the highestradiation dose due to these radionuclides (Table 2), as expected,validating the results of these calculations. Therefore, all analyzedwater sources do not offer health risk in terms of 222Rn and 220Rningestion, according to the dosimetric levels reported in this paper.

5. Conclusion

This study reported a comparative evaluation of the radioac-tivity due to 222Rn and 220Rn in several well-known Brazilianmineral waters occurring at São Paulo and Minas Gerais states.According to the Brazilian Code of Mineral Waters (BCMW)guidelines, three temperature categories were defined for theanalyzed waters, i.e. cold (<25 �C, 41 samples), hypothermal (25e33 �C, 33 samples) and mesothermal (33e36 �C, 1 sample). Theinvestigation was held also monitoring the presence of thefollowing dissolved gases: O2, CO2 and H2S. An inverse relationshipwas found between temperature and dissolved O2, indicating thatthe increasing temperature causes a decrease in dissolved O2 of theanalyzed waters. A trend of inverse relationship between temper-ature and dissolved CO2 was identified in the hypothermal andmesothermal waters, also indicating that its solubility decreasesaccompanying the temperature raising. According to the BCMWguidelines, 33 water sources were carbogaseous (contained dis-solved CO2 corresponding to a minimum of 200 mL per liter),whereas 3 were sulfured waters (contained dissolved sulfide cor-responding to a minimum of 1 mg/L). The 222Rn activity concen-tration range was 0.02e112.5 Bq/L, whereas the 220Rn activityconcentration range was <4e895 mBq/L. The highest 222Rn levelswere found in Boi and Villela springs located at Águas da Prata city(São Paulo State) and Dona Beja spring situated at Araxá city (MinasGerais State) that are sites characterized by the abundant presenceof natural radioelements in the rock matrices. A significant rela-tionship was found between dissolved radon and thoron in thehypothermal and mesothermal waters, perhaps related to tem-perature effects on the dissolution of their parents 226Ra and 224Rafrom the rock surfaces. According to the BCMWguidelines, none ofthe water sources were thoriferous (dissolved thoron lower than 2Mache unit/L), whereas the waters of Vitória and Boi springs wereweakly radioactive (222Rn levels between 5 and 10 Mache unit/L)and the waters of Villela and Dona Beja springs were radioactive(222Rn levels between 10 and 50 Mache unit/L). The waters of Vil-lela and Dona Beja springs exhibited 222Rn activity concentrationexceeding the WHO guidance level of 100 Bq/L in drinking-waterfor public water supplies, as well the maximum a-energy intakefor radon progeny corresponding to 0.4 � 10�3 J that is about 100times lower than the IAEA guideline reference value. Themaximumthoron progeny intake was 5 � 10�5 J for the geyser at Caxambucity, Minas Gerais State, that is almost 2600 times lower than theIAEA guideline value and circa 80 times lower than the maximuma-energy intake for radon progeny at Villela and Dona Beja springs.Thus, 220Rn doses were much lower than that of 222Rn and thecalculations in this paper indicated that all analyzedmineral watersdo not offer health risk in terms of these radionuclides ingestion asthe activity concentrations do not reach high enough values fortheir decay products to produce significant doses.

Acknowledgments

FAPESP (Foundation Supporting Research in São Paulo State)and CNPq (National Council for Scientific and Technologic

D.M. Bonotto / Journal of Environmental Radioactivity 132 (2014) 21e3030

Development) in Brazil are greatly acknowledged for financialsupport of this investigation. Two anonymous reviewers arethanked very much for helpful comments that improved thereadability of the manuscript.

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