adon concentration measurements were performed in indoor air and in natural mineral waters in seventeen Portuguese thermal spas used for therapy, drinking and irrigation purposes. The gamma doses rates were also assessed in different workplaces of the considered thermal spas. The radon concentration was measured in water samples taken from different sampling points: boreholes, springs, inhalator chambers (ORL’s) and swimming pools, and in the indoor air of different treatment rooms: ORL’s, swimming pools, vapours areas and Vichy shower. Radon concentration in water ranged from 26 to 6949 Bq/L and in the indoor air ranged from 73 Bq/m3 to 3479 Bq/m3. The indoor gamma dose rates ranged from 0,148 µSv/h to 0,644 µSv/h and the annual dose rate was estimated ranging from 0,30 to 1,29 mSv/y, for 2000 working hours per year, which is far below the effective dose limit for workers (20 mSv/y). Nevertheless, the great contribution for the annual effective dose will result from radon inhalation which is not included in this estimation. The remedial action level for drinking water of 1000 Bq/L (2001/928/ EURATOM) was exceeded in 23% of the selected thermal spas and about 80% of the total measurements of the indoor radon concentration exceeded the previous reference level of 200 Bq/m3 for new buildings and about 63% exceeded the new reference level of 300 Bq/m3 as established in the Directive 2013/59/EURATOM for indoor radon concentration in workplaces. Therefore, as the recommended limits for radon concentration in water and in indoor air were exceeded, appropriate actions should be taken in order to reduce the hazard to health from radon indoors and the potential resulting occupational exposure.

1. S. Alberigi, B.R. Pecequilo, H.A. Lobo and M.P. Campos, “Assessment of Effective Doses from Radon Levels for Tour Guides at Several Galleries of Santana Cave, Southern Brazil, with CR-39 Detectors: Preliminary Results,” Rad. Prot. Dos., vol. 145, no. 2-3, pp. 252–255, Mar. 2011.
   DOI: 10.1093/rpd/ncr054
2. Y. Yarar, T. Gunaydi, N. Celebi, “Determination of Radon Concentrations of the Dikili Geothermal Area in Western Turkey,” Rad. Prot. Dos., vol. 118, no. 1, pp.78–81, Feb. 2006.
   DOI: 10.1093/rpd/nci321
3. M. Erdogan, F. Ozdemir and N. Eren, “Measurements of Radon Concentration Levels in Thermal Waters in the Region of Konya, Turkey,” Isot. Environ. Health Stud., vol. 49, no. 4, pp. 567–574, Aug. 2013.
   DOI: 10.1080/10256016.2013.815182
4. T.O. Santos, Z. Rocha, P. Cruz, V.A. Gouvea, J.B. Siqueira and A.H. Oliveira, “Radon Dose Assessment in Underground Mines,” Rad. Prot. Dos., vol. 160, no. 1-3, pp. 120-123, Apr. 2014.
   DOI: 10.1093/rpd/ncu066
5. D. Nikolopoulos, E. Vogiannis, E. Petraki, A. Zisos and A. Louizi, “Investigation of the Exposure to Radon and Progeny in the Thermal Spas of Loutraki (Attica-Greece): Results from Measurements and Modelling,” Sci. of the Total Environ., vol.408, iss.3, pp. 495–504, Jan. 2010.
   DOI: 10.1016/j.scitotenv.2009.09.057
6. T. Vaupotic, T. Streil, S. Tokonami and Z.S. Zunic, “Diurnal Variations of Radon and Thoron Activity Concentrations and Effective Doses in Dwellings in Niska Banja, Serbia,” Rad. Prot. Dos., vol. 157, no. 3, pp. 375-382, 2013.
   DOI: 10.1093/rpd/nct145
7. A.S. Silva, M. L. Dinis and A. Fiuza, “Research on Occupational Exposure to Radon in Portuguese Thermal Spas,” in Occupational Safety and Hygiene II, P.M. Arezes et al., Eds., London, England: Taylor & Francis, 2014, ch. 57, pp. 323 -328.
   DOI: 10.1201/b16490-58
8. J. Nikolov et al., “Radon in Thermal Waters in South-East Part of Serbia,” Radiation Protection Dos., vol. 160, no. 1-3, pp. 239-243, 2014.
   DOI: 10.1093/rpd/ncu094
9. A. Koray, G. Akkaya, A. Kahraman and G. Kaynak, “Measurements of Radon Concentrations in Waters and Soil Gas of Zonguldak,” Rad. Prot. Dosim., vol. 162, no. 3, pp. 375-387, Nov. 2013.
   DOI: 10.1093/rpd/nct308
10. M.A. Ziane, Z. Lounis-Mokrani and M. Allab, “Exposure to Indoor Radon and Natural Gamma Radiation in Some Workplaces at Algiers, Algeria,” Rad. Prot. Dosim., vol. 160, no. 1-3, pp. 128-133, July 2014.
    DOI: 10.1093/rpd/ ncu058
11. N. Kavasi et al., “Effect of Radon Measurement Methods on Dose Estimation,” Rad. Prot. Dosim., vol. 145, no. 2-3, pp. 224-232, 2011.
    DOI: 10.1093/rpd/ncr044
12. F. Oner, I. Yigitoglu and H.A. Yalim, “Measurements of Radon Concentration in Spa Waters in Amasya, Turkey,” Rad. Prot. Dosim., vol. 157, no. 2, pp. 221-224, May 2013.
    DOI: 10.1093/rpd/nct130
13. K. Jile, M. Slezákova and J. Thomas, “Diurnal and Seasonal Variability of Outdoor Radon Concentration in the Area of the NRPI Prague,” Rad. Prot. Dosim., vol. 160, no. 1-3, pp. 57-61, 2014.
    DOI: 10.1093/rpd/ncu091
14. M. Moldovan et al., “Radon and Radium Concentration in Water from North-West of Romania and the Estimates Doses,” Rad. Prot. Dosim., vol. 162, no. 1-2, pp. 96-100, 2014.
    DOI: 10.1093/rpd/ncu230
15. G. Trabidou and H. Florou, “Estimation of doses rates to humans exposed to elevated natural radioactivity through different Pathways in the Island of Ikaria, Greece,” Rad. Prot. Dosim., vol. 142, no. 2-4, pp. 378-384, 2010.
    DOI: 10.1093/rpd/ncq269
16. M. Pugliese, M. Quarto and V. Roca, “Radon Concentra-tions in Air and Water in the Thermal Spas of Ischia Island,” Indoor and Built Environ., vol. 23, no. 6, pp. 823-827, 2013.
    DOI: 10.1177/1420326X13480053
17. S. Labidi, F. Essafi and H. Mahjoubi, “Estimation of the Radiological Risk Related to the Presence of Radon 222 in a Hydrotherapy Centre in Tunisia,” J. Radiol. Prot., vol. 26, no. 3, pp. 309-316, 2006.
    DOI: 10.1088/0952-4746/26/3/005
18. A.S. Silva and M. L. Dinis, “The Presence of Radon in Thermal Spas and their Occupational Implications – a review,” in Occupational Safety and Hygiene III, P. Arezes et al., Eds., London, England: Taylor & Francis, 2015, ch. 13, pp. 59 – 65.
    DOI: 10.1201/b18042-14
19. Standard Test Method for Radon in Drinking Water, ASTM D5072-09e1, 2009. Retrieved from: http://www.astm.org/DATABASE.CART/HISTORICAL/D5072-09E1.htm
20. R. Rusconi et al., “The Monitoring of Tap Waters in Milan: Planning Methods and Results,” Rad. Prot. Dosim., vol. 111, no. 4, pp. 373-376, 2004.
    DOI: 10.1093/rpd/nch057
21. C.V.M. Goncalves and A.J.S.C. Pereira, “Radionuclides in Groundwater of the Serra do Bucaco Region (Central Portugal),” in Proc. of the XXXV Congr. of the Int. Assoc. of Hydrogeol., Lisbon, Portugal, 2007, pp.
22. A. Louro et al., “Human Exposure to Indoor Radon: a Survey in the Region of Guarda, Portugal,” Rad. Prot. Dosim., vol. 154, no. 2, pp. 237-244, Apr. 2013.
    DOI: 10.1093/rpd/ncs166