Measurements of Radon Concentration Levels in Drinking Water at ...

2009 International Nuclear Atlantic Conference - INAC 2009 Rio de Janeiro,RJ, Brazil, September27 to October 2, 2009 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-03-8

Measurements of Radon Concentration Levels in Drinking Water at Urban Area of Curitiba (Brazil). Janine Nicolosi Corrêa1, Sergei A. Paschuk1, Hugo R. Schelin1, Laercio Barbosa1, Tatyana Sadula1, Cristiana A. Matsuzaki1 1

Federal University of Technology – Paraná, UTFPR Av. 7 de Setembro 3165, Curitiba - PR, Brazil

[email protected], [email protected]

ABSTRACT Current work presents the results of more than 100 measurements of 222Rn activity in drinking water collected at artesian bores at Curitiba region during the period of 2008 - 2009. The measurements were performed at the Laboratory of Applied Nuclear Physics of the Federal University of Technology in cooperation with the Nuclear Technology Development Center (CDTN) of Brazilian Nuclear Energy Committee (CNEN). Experimental setup was based on the Professional Radon Monitor (ALPHA GUARD) connected to specific kit of glass vessels Aqua KIT through the air pump. The equipment was adjusted with air flow of 0.5 L/min. The 222Rn concentration levels were detected and analyzed by the computer every 10 minutes using the software DataEXPERT by GENITRON Instruments. Collected average levels of 222Rn concentration were processed taking into account the volume of water sample and its temperature, atmospheric pressure and the total volume of the air in the vessels. Collected samples of water presented the average 222Rn activity about 57.70 Bq/L which is almost 5 times more than maximum level of 11.1 Bq/L recommended by the USEPA (United States Environmental Protection Agency). It has to be noted that many artesian drillings presented the radon activity in the range of 100 - 200 Bq/L. Further measurements are planned to be performed at other regions of Parana State and will involve the mineral water sources, explored artesian drillings as well as soil samples.

1. INTRODUCTION After the decades of systematic and numerous studies performed at different countries of the World, it is concluded that radon as well as its progeny is the main cause of lung cancer [1]. Radon is heavy noble radioactive gas produced in three principle radioactive series. Specifically, 222Rn is produced by the 238U decay series and proceeding from  -decay of 226 Ra [2,3]. It is well known that more than 50% of the effective annual radiation dose received by a human being is related to the radon and its progenies. Among the principle mechanisms that bring the radon inside the dwelling is the soil exhalation as well as exhalation and release from the water [2,3]. It was evaluated that considering the latest mechanism, the exhalation of radon from the water represents about 89% of the cancer risk and the consumption of water with high concentration of radon is related to about 11% of risk cancer [4]. Radon concentration in water could be subject of different factors such as the geology of the area, bottom sediments and inputs from streams, temperature, atmospheric pressure, etc. It is well known that the solubility of radon in water is about 510 cm3 kg-1 at 0oC and decreases at higher temperatures [5].

The 222Rn concentration in various types of natural water in different countries usually is about few Bq/L and is the subject of the National legislation as well as International norms and recommendations. For example, the United States Environmental Protection Agency (USEPA) established a limit of 11.1 Bq/L for the radon level in drinking water and this limit is considered as guideline in Canada and many countries of the European Union [6]. It has to be remembered a limit of radon activity in water established more than 15 years ago and reevaluated recently by the World Health Organization where 100 Bq/L was considered appropriate for public water supplies [4]. 2. MATERIALS AND METHODS Samples of water were collected at Curitiba urban area during the period of 2008 – 2009. The measurements were performed at the Laboratory of Applied Nuclear Physics of the Federal University of Technology – Paraná (UTFPR, Curitiba, Brazil) with the help of instant radon detector AlphaGUARD (Genitron Instruments) which is also suitable for continuous monitoring of radon concentrations in the range of 2 – 2*106 Bq/m³. This detector (pulsecounting ionization chamber suitable for alpha spectroscopy) is a portable, battery- or netoperated radon monitor with high storage capacity which records, using the integrated sensors, simultaneously with detected radon activity the ambient temperature, relative humidity and atmospheric pressure. The water samples were placed in appropriate system of glass vessels (Aqua KIT) connected to detector through the pump which following the recommendations of the manufacturer [7] and previously performed methodological studies [8] was adjusted to 0.5L/min. Figure 1 shows the AlphaGUARD detector in measurements with water sample.

Figure 1 - Detector AlphaGUARD (Genitron Instruments) in measurements of radon activity concentration in water. The radon concentration in water was received by the equation (1) involving various ambient characteristics such as the temperature of the environment and the diffusion coefficient (K) correlated to the temperature. INAC 2009, Rio de Janeiro, RJ, Brazil.

Cair ( Cwater 

Vsistem  Vsample  K )  Cbg Vsample 1000

(1)

Where:  Cwater is the radon concentration in water sample [Bq/L];  Cair is the radon concentration [Bq/m3] in the air of the system after radon release the water;  Cbg is the radon concentration before the beginning of the measures (background)  Vsystem is the total volume [mL] of the complete system;  Vsample is the water sample volume [mL];  K is the diffusion coefficient which as a function of water sample volume and its temperature and the volume of the air in the system was calculated following the semi-empirical equation (2), recommended by AlphaGUARD manual [7]: K  0.105  0.405  e  0.502  T ( C ) o

(2)

The collection of the water samples of the wells was made using 500ml PET bottles from the depth about 1.5m below the level of water surface in the well. Completely filed PET bottles were tightly closed to prevent the entry of air into the bottle as well as to prevent the release of radon from it. The sealed samples were transported to the Laboratory of Applied Nuclear Physics of the Federal University of Technology – Paraná (UTFPR, Curitiba, Brazil) to be submitted minimum delay to the radon concentration measurements. When the time delay between the sample collection and measurements was significant, the correction was introduced using the equation (3).

C0 

C (t ) e  t

(3)

Where C0 is the calculated initial radon activity [Bq/L] of the sample; C(t) is the measured activity [Bq/L] at the time t after the sample was collected, and  is the decay constant for 222 Rn.

3. RESULTS AND CONCLUSIONS Obtained results concerning the average concentration of 222Rn in drinking water samples collected at artesian drills at Curitiba Metropolitan Area, together with associated errors are presented in Table 1. Comparing present data with other experimental results obtained at Brazil (mainly at São Paulo, Minas Gerais and Rio de Janeiro States) [9 - 20] it could be concluded that the range of measured radon concentrations is similar. It can be seen that the biggest part of the water samples (more than 75%) presented the values of radon activity above the limit value of 11.1 Bq/L, recommended by the United States Environmental Protection Agency (USEPA) [6]. As

INAC 2009, Rio de Janeiro, RJ, Brazil.

well as the average of obtained data of 57.70 Bq/L is 5 times bigger than recommended value for radon concentration in water.

Table 1. Results of the concentration of 222Rn activity in water samples of wells at Curitiba (Brazil) WATER SAMPLES COLLECTED AT CURITIBA URBAN AREA Region 1 Region 2 Region 3 Region 4 Region 5 Region 6 Region 7 Region 8 Region 9 Region 10 Region 11 Region 12 Region 13 Region 14 Region 15 Region 16 Region 17 Region 18 Region 19 Region 20 Region 21 Region 22 Region 23 Region 24 Region 25 Region 26 Region 27 Region 28 Region 29 Region 30 Region 31 Region 32 Region 33 Region 34


AVERAGE 222Rn CONCENTRATION (Bq/L) 1.88 6.40 2.26 1.28 6.10 4.34 9.46 23.05 103.82 106.63 27.33 195.97 18.75 41.78 114.30 91.04 184.62 26.58 49.42 76.03 47.90 31.60 5.25 24.07 112.12 152.25 168.00 46.23 16.70 48.91 44.14 60.19 55.05 58.30

Error (Bq/L) 3.90 2.50 1.39 4.02 3.17 4.90 14.68 31.52 24.49 10.04 38.94 7.37 19.03 9.17 14.73 17.46 13.51 11.67 3.57 8.65 27.45 39.11 45.57 15.48 17.91 35.12 36.78 18.02 17.46 19.09

In the nearest future it is planned to perform the measurements of natural radionuclides from uranium decay series with an objective to compare obtained data with radionuclides concentration in the soil as well as to compare measured values with previously obtained results within similar geological regions of Brazil.

ACKNOWLEDGMENTS The authors are very thankful to CNPq, CNEN and Fundação Araucária (Paraná St.) for financial support of this work as well as to colleagues from the Institute of Radiation Protection and Dosimetry (IRD/CNEN) and from the Center of Nuclear Technology Development (CDTN/CNEN) for permanent positive discussions and assistance in the measurements.

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