Internal effective dose assessment for the public based on the environmental radioactivity data in Portugal

Radiation Physics and Chemistry 168 (2020) 108558

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Internal effective dose assessment for the public based on the environmental radioactivity data in Portugal

T

M.J. Madrugaa,b,∗, A.R. Gomesb, J. Abrantesb, M. Santosa,b, E. Andradea,b, A. Mouratob, A. Libâniob, M. Reisa,b a b

Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, km 139,7, 2695-066, Bobadela LRS, Portugal Laboratório de Proteção e Segurança Radiológica, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, km 139,7, 2695-066, Bobadela LRS, Portugal

A R T I C LE I N FO

A B S T R A C T

Keywords: Environmental radioactivity 7 Be 137 Cs 210 Pb inhalation 3 H 90 Sr 222 Rn ingestion Internal effective dose Portuguese population

The objective of this work is to estimate the internal effective dose to the Portuguese population due to the radionuclides inhalation (through the air) and the radionuclides intake (through the ingestion of milk, foodstuffs and drinking water) during the year 2017. In the framework of the environmental radioactivity monitoring performed in Portugal, samples of aerosol particles, milk, foodstuffs (individual products and two complete meals, lunch and dinner, corresponding to one-day intake) and drinking water were collected in mainland of Portugal and in Madeira and Azores Islands. After laboratory preparation, the samples were analysed for radionuclides using appropriate radioanalytical techniques. Among the analysed radionuclides, 137Cs, 90Sr and 3 H presented very low activity values, and the majority of their activities was below the minimum detectable activities. The natural radionuclides 7Be and 210Pb were detected in the aerosol particles and the 222Rn in drinking water samples. The internal effective dose was calculated considering the radionuclides activity concentrations, the radionuclides conversion factors and either, the Portuguese annual consumption rate for an adult or, the European annual intake rates for three age categories (infant, child and adult). The calculated effective dose, in both cases, corresponds to about 1% of 1 mSv year−1, the limit for public exposure. Therefore, the inhalation and ingestion of the studied radionuclides do not constitute any risk to the health of the Portuguese population and, so, it can be concluded that there is no need to recommend any radiological protection measures.

1. Introduction To comply with the recommendations set forth in Articles 35 and 36 of the Euratom Treaty, the Instituto Superior Técnico (IST) has been performing every year the environmental radioactivity surveillance in Portugal (Decree-Law 138/2005 of August 17th). Since December 2018, after the transposition of the European Directive 2013/59/ Euratom to the Portuguese regulation, these obligations are now attributed to the Agência Portuguesa do Ambiente (APA) (Decree-Law 108/2018 of December 3rd, Art° 13°). The main objective of this environmental monitoring programme is the determination of artificial and natural radionuclides in environmental compartments (air, water, soils, etc.) and foodstuffs, which are considered the main radionuclides transfer pathways to humans (Madruga, 2008). Portugal is a non-nuclear country but it is subject to the influence of the nuclear power plants in the neighbouring country, Spain. Therefore, this monitoring

programme was defined according to the specificities of the country concerning the sampling locations, frequency and type of samples. Following the atmospheric nuclear weapons tests and the nuclear accidents (Chernobyl and Fukushima) the artificial radionuclides, cesium137 (137Cs) and strontium-90 (90Sr), were spread worldwide and deposited in the environment thus interacting with the plants, through direct deposition on the leaves or, indirectly by absorption, through the roots. The radionuclides accumulated in plants, mainly 137Cs and 90Sr can be transferred to animals and consequently to human beings through the consumption of animal-derived products such as milk and meat. As the radionuclides 137Cs and 90Sr are chemically similar to potassium and calcium, respectively, they are metabolized in the human body. In addition to these radionuclides, the tritium (3H) from natural and anthropogenic origin can also be deposited or discharged during the normal operation of nuclear power installations in surface waters (rivers, lakes, etc.). These waters, when used for human

∗ Corresponding author. Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, km 139,7, 2695-066, Bobadela LRS, Portugal. E-mail address: [email protected] (M.J. Madruga).

https://doi.org/10.1016/j.radphyschem.2019.108558 Received 29 July 2019; Received in revised form 7 October 2019; Accepted 31 October 2019 Available online 02 November 2019 0969-806X/ © 2019 Elsevier Ltd. All rights reserved.

Radiation Physics and Chemistry 168 (2020) 108558

M.J. Madruga, et al.

consumption, become a radioactive transfer pathway to humans. The potassium-40 (4 K) is uniformly distributed in the body following food intake, and its concentration in the body is under homeostatic control. For adults, the body content of potassium is about 0.18%, and for children, about 0.2% (UNSCEAR, 2000). The human internal radiation exposure due to these radionuclides depends on the radionuclide activity concentrations in the air inhaled and the foodstuffs ingested and on the inhalation and consumption rates, respectively. The contribution of the different pathways for human radiation doses depend on different factors in the case of internal radiation exposure: i) type of radionuclide release (atmospheric, aquatic); ii) radionuclide and its chemical composition (half-life, radiation type and energy, environmental mobility and bioavailability); iii) environmental conditions (climate, soil type, season, etc.); iv) habits of the exposed population (food preferences, etc.); and, v) agricultural practices (plant/animal breeding, crops, etc.) (Balonov, 2008). In this study, the internal radiation dose to the Portuguese population was estimated taking into account the inhalation and ingestion of radionuclides existing in the air inhaled (airborne particles) and in the milk, foodstuffs (individual products and complete meals) and drinking waters intake. For inhalation, airborne particulates, which represent a highest radiological significance, were sampled, by pumping air through filters, using an aerosol sampling station located in a location representative of the country. For ingestion, milk, which is considered one of the main pathways for uptake of radionuclides from the environment to human, was taken from the main dairies covering large geographical areas of the country. Concerning foodstuffs, individualized products were selected and sampled around the country in order to represent as much as possible the composition of the Portuguese diet. Complete meals from a large local consumption were also taken to give a representative figure of mixed diet. Drinking water was sampled in a city representing a larger number of consumers. The annual effective dose obtained was compared with the dose limit to the public, taking into account reference and Portuguese diet habits.

Fig. 1. Sampling locations in mainland of Portugal and in Madeira and Azores Islands.

2. Materials and methods The stability of the measuring chain (activity, FWHM, centroid) was checked once a week with a europium-152 (152Eu) certified point source.

2.1. Air monitoring (aerosol particles) Radioactivity in air is monitored by collecting aerosol particles using an aerosol sampling station type ASS-500 (Physik Technic Innovation), located at the IST campus in Sacavém. The sampling station is equipped with a high volume suction pump, a continuous flow meter and an air volume accumulator. The air is filtered through a 44 cm × 44 cm filter (Petrianov type FPP-15-1.5) with an air volume flow rate of 800 m3 h−1, on average. The filters, exchanged weekly, are folded and pressed using a hydraulic press to fit a cylindrical geometry (5 cm diameter and 1 cm thickness). The activity concentrations in beryllium-7 (7Be), 137Cs and lead-210 (210Pb) were determined by high resolution gamma spectrometry on HPGe detectors. The detection efficiency was determined using NIST-traceable multi-gamma radioactive standards (POLATOM Laboratory of Radioactivity Standards) with energy photo-peaks ranging from 46.5 keV (210Pb) to 1836 keV (88Y) customized to reproduce exactly the geometries of the samples. The calibration source for water, milk and foodstuffs samples (geometry Marinelli) was prepared in a water-equivalent epoxy resin matrix (density of 1.15 g cm−3). For efficiency calibration of the filter geometry, the same type of filter as the one used at the aerosol sampling station was contaminated, with a mixture of radionuclides (NISTtraceable multi-gamma radioactive standards) and pressed to fit the same geometry of a normal aerosol sample. The Genie 2000 (version 3.4) software® was applied for the data acquisition and spectral analysis. The GESPECOR (version 4.2) software® (Sima et al., 2001) was used for matrix corrections (self-attenuation) and coincidence summing effects, as well as to calculate the efficiency transfer factors from the calibration geometry to the measurement geometry (whenever needed).

2.2. Milk and foodstuffs Raw milk samples were collected in mainland Portugal directly from the dairies reservoirs on a monthly basis at Vila do Conde and Portalegre and quarterly at Tocha- Cantanhede and Águas de Moura. Concerning Azores and Madeira Islands, the samples were purchased directly from the producer twice a year (Fig. 1). The individual foodstuffs samples (meat, tubers, vegetables and fruits) were randomly collected at producers in mainland of Portugal and in Azores and Madeira Islands (Fig. 1). One sample of mixed diet (two complete meals, lunch and dinner, corresponding to one-day intake) was collected monthly at a University canteen of Lisboa (Fig. 1). One liter of milk was transferred directly to a Marinelli beaker. Each sample of foodstuff and mixed diet was prepared, mixed, homogenized and transferred to a 1-L Marinelli beaker. The 137Cs and 4 K activity concentrations in milk and foodstuff samples were determined by gamma-ray spectrometry using HPGe detectors, as described previously in 2.1. The 90Sr was isolated from the other interfering elements using a strontium-specific resin (EICHROM) after incineration of the samples and dilution in an acid medium. The beta measurement in the liquid phase was performed by liquid scintillation counting using a PerkinElmer Tri-Carb 3170 TR/SL spectrometer. The 90Sr activity concentration was determined after the radioactive balance between 90 Sr and its daughter 90Y (Lopes and Madruga, 2009a; 2009b; Lopes et al, 2010, 2014). 2

Radiation Physics and Chemistry 168 (2020) 108558

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2.3. Drinking water

2.5. Calculations of internal radiation dose

Drinking water samples were collected monthly in Lisboa (Fig. 1) and were analysed, among others, for 137Cs, 90Sr, 3H and radon-222 (222Rn). Thirty liters of acidified water were concentrated to 1 L (by slow evaporation and acid digestion on an electric plate) and measured for 137Cs, in 1-L Marinelli beaker, by gamma-ray spectrometry as described previously in 2.1. After measurement, the water was evaporated to dryness (white residue). A radiochemical technique was applied to the residue, based on successive separations and purifications of the sample. The strontium is separated from the carbonate precipitate using a specific resin (100–150 μm Sr–C50-A from EICHROM) and stored until the radioactive balance between 90Sr and the 90Y (20 days) was attained. The 90Y was measured after the 90Sr separation in the form of yttrium oxide, using a gaseous flow proportional counter, Tennelec (Canberra) XLB-S5. The 3H activity in the water samples was determined by electrolytic enrichment followed by liquid scintillation counting measurements. One liter of water is purified by vacuum distillation before measurement in order to remove any impurities and interfering radionuclides to reduce quenching. Distillation is performed by adding 0.5 g of Na2S2O3 and 1 g of Na2CO3 to a water volume of about 500 mL. The electrolytic enrichment is carried out by adding 1 g of sodium peroxide (Na2O2) to a water sample aliquot of 250 mL (the sodium hydroxide formed is used as electrolyte). The electrolytic enrichment system is cooled to a temperature of about 2 °C. The 250 mL of water sample in the electrolytic cell is submitted to an electrical charge until the reduction of the sample to a mass of about 15 g. Afterwards the sample is neutralized by adding lead chloride (PbCl2) and distilled again in order to separate the lead oxide (PbO) and other impurities from the water. An aliquot of the distillate (8 g) is mixed with 12 g of Ultima Gold LLT™ scintillation cocktail in High Performance borosilicate Glass Vials™ (PerkinElmer). The measurements are performed during 300 min in a Tri-Carb 3170 TR/SL (PerkinElmer) liquid scintillation counter in low-level mode (Gomes et al., 2017). The 222Rn determination was performed in compliance with the ISO 13164–4:2015 liquid scintillation counting standard. The 222Rn is extracted from the aqueous solution through a water-immiscible scintillation liquid that has high radon solubility. An aliquot of 10 g of water is withdrawn from a flask, with the aid of a syringe, taking care to collect the aliquot below the surface of the water without turbulence. The needle of syringe is inserted into the scintillation vial and the sample is slowly injected below the 10 g of scintillation liquid (Opti Fluor O™) surface without causing turbulence, in order to minimize any loss of radon. After transferring the sample, the scintillation vial is immediately closed and is weighed to determine the mass of the sample (the date of preparation was recorded). Before measurement, the sample is stored in dark for 3 h until equilibrium is reached between 222 Rn and its short-lived progeny (218Po, 214Pb, 214Bi and 214Po). The 222 Rn activity is measured during 120 min in a liquid scintillation counter in low-level mode (Tri-Carb 3170 TR/SL).

The annual effective dose, which represents the health risk to the whole body due to radionuclides inhalation was estimated using the following formula (UNSCEAR, 2000):

Dinh = Cair , i × Rinh × FDinh, i

(1) −1

where, Dinh is the annual effective dose (Sv year ) to an individual due to the inhalation of radionuclides; Cair,i is the radionuclide activity concentration in air (Bq m−3); Rinh is the inhalation rate (m3 year−1); FDinh,i is the inhalation dose conversion factor (Sv Bq−1) for the radionuclide i, considering the category of member of the public. Similarly, the annual effective dose due to the intake of radionuclides in drinking water and foodstuffs was also estimated using the following expression (UNSCEAR, 2000; European Directive, 2013/51 Euratom):

Ding = Ci, j × Qj × FDi

(2) −1

where, Ding is the annual effective dose (Sv year ) to an individual due to the ingestion of radionuclides; Ci,j is the radionuclide activity concentration in drinking water/foodstuff j (in Bq L−1 or Bq kg−1); Qj is the annual consumption rate per capita (L year−1 or kg year−1) of drinking water/foodstuff j; FDi is the dose conversion factor (Sv Bq−1) for the ingested radionuclide i, considering the category of member of the public. The effective dose is strongly dependent on the drinking water and the foodstuff consumption amounts. In both cases, the dose conversion factor depends on the radionuclide and on the age of the individual (IAEA, 2014). The total dose was obtained through the sum of the contributions of each radionuclide in the samples. 3. Results and discussion 3.1. Radionuclide activity concentrations 3.1.1. Aerosol particles Table 1 shows the activity concentration values (mBq m−3) of 7Be, 137 Cs and 210Pb in aerosol particles collected in Sacavém during the year 2017. The 7Be and 210Pb were detected in all the samples with values ranging from 1.02 ± 0.10 mBq m−3 to 6.25 ± 0.63 mBq m−3 and from 0.120 ± 0.013 mBq m−3 to 1.10 ± 0.12 mBq m−3, respectively. These values are coherent with those reported for the same location between the years 2001–2010 (Carvalho et al., 2013). The 137 Cs activity concentration values are below 1.1x10−3 mBq m−3, the minimum detectable activity (MDA). These values are consistent with the range of activity concentrations reported by other authors for different countries (Hernandez et al., 2007; Heinrich et al., 2007; Vallés et al., 2009; Abe et al., 2010; Pan et al., 2011; Dueñas et al., 2011; Leppänen et al., 2012). 3.1.2. Milk and foodstuffs The activity concentration values (Bq L−1) of 137Cs, 90Sr and 4 K in milk during the year 2017 are shown in Table 2. Regarding 137Cs, no measurable values were detected, all values were lower than the MDA (0.13 Bq L−1). The 90Sr detectable activity concentrations, ranged from

2.4. Quality assurance The laboratory participates regularly in intercomparison exercises organized by international institutions (Meresová and Watjen, 2013; IARMA ETRIT-PT-2014; Altzitzoglou and Malo, 2017; Björklöf, 2017). The techniques presented in this work for the determination of gammaemitter radionuclides by high-resolution gamma spectrometry (HPGe) in solid and liquid matrices and for the 222Rn determination in drinking waters by liquid scintillation counting are accredited by the Portuguese Accreditation Institute (IPAC) in compliance with EN ISO/IEC 17025:2005 standards.

Table 1 Activity concentration values, A ± 2σ (mBq m−3) for 7Be, 137Cs and 210Pb in air (aerosols) collected in Sacavém during the year 2017. Air (Aerosols)

7

Maximum Minimum MDA Values < MDA Number of samples

6.25 ± 0.63 1.02 ± 0.10 < 9.9x10−3 0 12

Be

MDA- Minimum detectable activity. 3

137

Cs

– – < 1.1x10−3 12 12

210

Pb

1.10 ± 0.12 0.120 ± 0.013 < 2.4x10−2 0 12

Radiation Physics and Chemistry 168 (2020) 108558

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Table 2 The 137Cs, 90Sr and 4 K activity concentration values ( ± 2σ) in milk and foodstuff samples collected in the mainland of Portugal and Azores and Madeira Islands and complete meals from a University canteen of Lisboa, during the year 2017. Milk (Bq L−1)

137

90

– – < 0.13 35 35

0.064 ± 0.027 0.016 ± 0.009 < 0.037 22 35

53.1 ± 4.2 43.2 ± 3.5 < 3.0 0 35

137

90

4

Cs

Maximum Minimum MDA Values < MDA Number of samples Foodstuffs-Individual products (Bq kg−1, f. w.)

Cs

Sr

Sr

4

K

K

Meat (cow, pork, etc.)

Maximum Minimum MDA Values < MDA Number of samples

– – < 0.14 15 15

0.082 ± 0.049 0.060 ± 0.032 < 0.081 12 14

117 ± 8 91.1 ± 6.6 < 3.2 0 15

Tubers (potatoes, onion, etc.)

Maximum Minimum MDA Values < MDA Number of samples

0.137 ± 0.073 0.137 ± 0.073 < 0.15 12 13

– – – – –

172 ± 12 35.3 ± 3.5 < 4.2 0 14

Fruits (orange, apple, pear, etc.)

Maximum Minimum MDA Values < MDA Number of samples

– – < 0.12 15 15

– – – – –

73.0 ± 5.5 19.0 ± 2.2 < 3.2 0 15

Vegetables (cabbage, lettuce, etc.)

Maximum Minimum MDA Values < MDA Number of samples

– – < 0.32 13 13

0.140 ± 0.015 0.049 ± 0.015 < 0.059 7 10

117 ± 9 31.1 ± 3.0 < 6.0 0 13

137

90

4

– – < 0.11 11 11

0.080 ± 0.047 0.057 ± 0.033 < 0.103 9 11

71.1 ± 5.0 35.2 ± 2.7 < 2.1 0 11

137

90

4

– – < 0.16 11 11

0.100 ± 0.061 0.049 ± 0.031 < 0.154 9 11

Foodstuffs-Complete meals (Bq kg−1, f. w.)

Cs

Maximum Minimum MDA Values < MDA Number of samples Foodstuffs-Complete meals (Bq d−1p−1, f. w.)

Cs

Maximum Minimum MDA Values < MDA Number of samples

Sr

Sr

K

K

110.4 ± 15.1 34.8 ± 7.9 < 3.0 0 11

MDA- Minimum detectable activity.

0.016 ± 0.009 Bq L−1 to 0.064 ± 0.027 Bq L−1, the same order of magnitude as the MDA (0.037 Bq L−1). It can be noticed that 4 K was detected in all samples with values three order of magnitude higher when compared to the other radionuclides. The values are relatively constant varying between 43.2 ± 3.5 Bq L−1 and 53.1 ± 4.2 Bq L−1. The mean values for 137Cs and 90Sr reported for Finland in 2017 (STUKB, 226, 2018) range between 0.19 Bq L−1 and 0.64 Bq L−1 and between 0.022 Bq L−1 and 0.029 Bq L−1, respectively. The 137Cs, 90Sr and 4 K activity concentration values (Bq kg−1, fresh weight) for the individual foodstuff products collected during the year 2017 are also presented in Table 2. All the results for 137Cs are below the MDA (ranging from 0.12 Bq kg−1 to 0.32 Bq kg−1) except for one sample (potatoes) which value is 0.137 ± 0.073 Bq kg−1. The 90Sr was only determined in the meat and vegetables samples. The majority of the 90Sr activity concentration values are below the MDA, presenting values lower than 0.081 Bq kg−1 for meat and lower than 0.059 Bq kg−1 for vegetables. The measurable values are in the same order of magnitude of maximum values of 0.082 ± 0.049 Bq kg−1 for meat and 0.140 ± 0.015 Bq kg−1 for vegetables (cabbage). As observed for milk,

the 4 K was detected in all foodstuff samples and the values are much higher when compared to the other radionuclides. For instance, values ranging from 19.0 ± 2.2 Bq kg−1 to 73.0 ± 5.5 Bq kg−1 and from 35.3 ± 3.5 Bq kg−1 to 172 ± 12 Bq kg−1 were obtained for fruits and tubers, respectively. Regarding the complete meals (Table 2) the radionuclides activity concentrations are of the same order of magnitude as those obtained in individual foodstuff products. Other authors (RIFE-23, 2018) reported values lower than 0.06 Bq kg−1 and 0.037 Bq kg−1 for 137Cs and 90Sr respectively in meals from canteens in England. For complete meals, that give a more precise information for radionuclides uptake via foodchain, seems more appropriate to estimate the activity consumed per day per person (Bq d−1p−1). Maximum values of 0.16 Bq d−1p−1, 0.100 ± 0.061 Bq d−1p−1 and 110.4 ± 15.1 Bq d−1p−1 were observed for 137Cs, 90Sr and 4 K respectively (Table 2). For 4 K, the value is slightly higher than the typical value 100 Bq d−1p−1 reported for European countries (De Cort et al., 2018).

4

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Table 3 Activity concentration values, A ± 2σ (Bq L−1) for

137

Cs,

137

Drinking water

Sr, 3H and

222

Rn in drinking water collected in Lisboa, during the year 2017. 90

Cs

– – < 3.6x10−3 12 12

Maximum Minimum MDA Values < MDA Number of samples

90

3

Sr −3

(2.87 ± 0.87)x10 (1.15 ± 0.59)x10−3 < 1.3x10−3 0 12

H

1.28 ± 0.26 0.44 ± 0.25 < 0.47 9 12

222

Rn

1.63 ± 0.39 0.50 ± 0.29 < 0.43 10 12

MDA-Minimum detectable activity.

detectable activity, this value would be considered as the maximum value. This option leads to an overestimation of the effective dose values. For the dose calculation via ingestion (eq. (2)) the maximum activity concentrations values of 137Cs and 90Sr (Table 2) and 137Cs, 90Sr, 3 H and 222Rn (Table 3) were used. As before, the same criteria concerning the use of maximum values was applied. Regarding the ingestion rate (annual consumption per capita) for the food chain products, two approaches were considered for the dose calculation: one, taking into account the national consumption rate for adult of the Portuguese population, as close as possible of local habits (Table 4) and, the other one, considering the European rates (ICRP, 2006) for three age categories (infant, child and adult) (Table 5). At the national level, data are not available for infant and child. Regarding the drinking water consumption, the value proposed in the European Directive (2013/51 Euratom) and adopted in Portugal (Decree-Law 152/2017) was used (Table 4). The 137Cs, 90Sr and 3H ingestion dose conversion factors for the three age categories (infant, child and adult) are published in IAEA, 2014. For 222Rn, the dose conversion factor value for adult, 3.5 nSv Bq−1 (NRC, 1999) was considered. In Fig. 2, it can be observed that the main contribution to the dose via inhalation is attributed to the natural radionuclide 210Pb (almost 100%). Regarding the artificial radionuclides 137Cs and 90Sr, the effective dose via milk intake is similar for both the radionuclides (around 50%) and higher for 90Sr (around 70%) via complete meals intake. Concerning the drinking water ingestion, the main contribution is attributed to the natural radionuclide 222Rn (97.4%) followed by 90Sr (1.4%), 137Cs (0.8%) and 3H (0.4%). It should be emphasized that in spite of the 222Rn and 3H activity concentration values are similar (Table 3) the contribution of 222Rn to the effective dose is much higher than the one for 3H. This results from the dose conversion factor values that are two order of magnitude higher for 222Rn (3.5x10−9 Sv Bq−1) when compared to 3H (1.8x10−11 Sv Bq−1). This means that for the same activity value, higher damage is caused by 222Rn in the body. The estimated annual internal effective dose for the Portuguese population due to the inhalation and ingestion of radionuclides present in air, milk, complete meals and drinking water is 17.0 μSv year−1. The contribution of the individual foodstuff products to the effective dose was not considered in this calculation since the complete meals are more representatives of the foodstuffs human intake. The main contribution is due to the air inhalation (9.97 μSv year−1), followed by the radionuclides intake via drinking water (4.27 μSv year−1), complete meals (2.33 μSv year−1) and milk (0.41 μSv year−1) (Table 4). This estimated value is lower (about two orders of magnitude) than 1 mSv year−1, the maximum dose limit allowed for the category of member of the public (European Directive, 2013/59/Euratom). The annual internal effective dose for the Portuguese population was also estimated for three age categories (infant, child and adult) taking into account the European inhalation rates and the foodstuff consumption rates (Table 5). It can be observed that the inhalation effective dose increase from infant to adult accordingly to the inhalation rates increase. On the contrary, the effective dose via milk intake decreases from infant (1.99 μSv year−1) to child (1.23 μSv year−1) and adult (0.836 μSv year−1). This finding is due to the milk consumption

3.1.3. Drinking water The 222Rn, 137Cs, 90Sr and 3H activity concentration values (Bq L−1) in drinking water for the year 2017 are shown in Table 3. The 137Cs activity concentrations are below the MDA value, 3.6 mBq L−1. The 90 Sr was detected in all the samples with values ranging from 1.15 ± 0.59 mBq L−1 to 2.87 ± 0.87 mBq L−1. Values of the same order of magnitude for 137Cs and 90Sr, ranging from 0.1 mBq L−1 to 13 mBq L−1, were reported for drinking water in Finland (STUK-B, 226, 2018). The 3H activity levels detected in drinking water samples ranged between 0.44 ± 0.25 Bq L−1 and 1.28 ± 0.26 Bq L−1, far below the limit of 100 Bq L−1 that has been set for 3H in drinking water (European Directive, 2013/51 Euratom; Decree-Law 152/2017). The highest activity concentration value (1.63 ± 0.39 Bq L−1) was obtained for 222Rn. This value is however two orders of magnitude lower than the limit of 500 Bq L−1 in force in Portugal for 222Rn in drinking water (Decree-Law 152/2017).

3.2. Internal effective dose The annual effective dose via inhalation was calculated (eq. (1)), for the year 2017, considering the 7Be, 137Cs and 210Pb maximum activity concentration values (Table 1), the inhalation rate for adult (ICRP, 2006) and the inhalation dose conversion factors of 2.1x10−10 Sv Bq−1, 5.4x10−9 Sv Bq−1 and 3.7x10−6 Sv Bq−1 for 7Be, 137Cs and 210Pb respectively, applied to an adult belonging to the category of member of the public (IAEA, 2014). The results are presented in Table 4. According to the radiological protection principle, it was postulated conservatively that in the cases where the values are lower than the minimum Table 4 Annual effective dose (μSv year−1) for the Portuguese population due to the inhalation and the ingestion of radionuclides present in air, foodstuffs (individual products, complete meals) and drinking water considering the inhalation rate and the Portuguese annual consumption for one adult, member of the public. Annual effective dose (μSv year−1) Air

Inhalation rate 8234 m3 year−1 (*)

Annual consumption Milk 117.4 kg year−1 (**) Foodstuffs-Individual products Meat 18.9 kg year−1 (**) Tuber 93.5 kg year−1 (**) Fruit 130 kg year−1 (**) Green vegetable 107.5 kg year−1 (**) Total – Foodstuffs-Complete 0.8–1 kg d−1 p−1 meals Drinking water 730 L year−1 (***)

9.97

0.41 0.078 0.166 0.203 0.869 1.32 2.33 4.27

*ICRP, 2006. **data collected from Portuguese database, Instituto Nacional de Estatística, Statistics Portugal, 2019, https://www.ine.pt/xportal/xmain?xpid=INE& xpgid=ine_indicadores&indOcorrCod=0000214&selTab=tab2&xlang=pt. ***European Directive 2013/51 Euratom; Decree-Law 152/2017. 5

Radiation Physics and Chemistry 168 (2020) 108558

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Table 5 Annual effective dose (μSv year−1) for the Portuguese population due to the inhalation and ingestion of radionuclides present in air, milk and individual foodstuff products, considering the inhalation rates and foodstuff consumption values for infant, child and adult in Europe (ICRP, 2006).

Air (inhalation rate, m3 year−1) Milk (kg year−1) Green vegetable (kg year−1) Beef (kg year−1) Total

Infant (1-year old)

Annual effective dose (μSv year−1)

Child (10-yearold)

Annual effective dose (μSv year−1)

Adult

Annual effective dose (μSv year−1)

1927 320 30 20

7.84 1.99 0.422 0.153 10.4

5606 240 35 30

9.25 1.23 0.406 0.189 11.1

8234 240 80 45

9.97 0.836 0.646 0.185 11.6

and the dose conversion factors that are higher for infant. For green vegetables, the effective dose is higher for adult (0.646 μSv year−1) since the consumption is also much higher. Concerning the meat (beef), the values are similar for child and adult and slightly higher than those obtained for infant. For the three age categories, the main contribution to the effective dose is due to the radionuclides inhalation and to the milk intake. The effective dose balance indicates no significant difference between the three age categories with values of 10.4 μSv year−1, 11.1 μSv year−1 and 11.6 μSv year−1 for infant, child and adult respectively. As before, these values are two orders of magnitude lower than the maximum dose limit allowed for the category of member of the public (1 mSv year−1).

drinking water intake mainly related to the presence of the natural radionuclides. No significant difference was observed for the effective dose values for the three age categories. These results show no significant radiation dose and no risk to the health of the Portuguese population. Therefore, there is no need to recommend any radiological protection measures.

4. Conclusions

Acknowledgments

The activity concentration values for 137Cs, 90Sr and 3H determined in the different samples are very low, the majority of them below the MDA. The natural radionuclides, 7Be and 210Pb, and 222Rn were detected in aerosol particles and in drinking water respectively. However, the values are low, being in the case of 222Rn, about two orders of magnitude lower than the limit in force in Portugal (500 Bq L−1). The estimated effective dose for the Portuguese population, considering either, the national consumption rate for adult or, the European consumption rate for three age categories (infant, child and adult) represents about 1% of the dose limit for a member of the public. The main contribution to the dose is due to the air inhaled and the

The authors would like to thank: i) The Food and Economic Security Authority (ASAE) that proceed to the collection of milk and food products in the mainland of Portugal (collaborative protocol between IST and ASAE); ii) The Regional Inspection of the Economic Activities from Azores Island and the Regional Secretariat for the Environment and Natural Resources of Madeira Island for the support provided in the collection and dispatch of food samples from the respective regions; iii) The dairy companies Lactogal, Serraleite and Parmalat Portugal Lda, for making available the milk samples; iv) The Social Services of the Lisboa University (SASUL) for the

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Fig. 2. Contribution fraction of individual radionuclides to effective dose of inhalation (137Cs, 7Be, 210Pb) and to effective dose for consumption of milk and complete meals (137Cs, 90Sr) and drinking water (137Cs, 90Sr, 3H, 222Rn). 6

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