Abstract â The results are presented of 83 measurements of radon (222Rn) in drinking water in Garhwal Himalaya, Northern. India. The results are compared ...
TECHNICAL NOTE
Radiation Protection Dosimetry Vol. 74, Nos. 1/2, pp. 103–105 (1997) Nuclear Technology Publishing
MEASUREMENT OF RADON IN DRINKING WATER AND INDOOR AIR R. C. Ramola†, R. B. S. Rawat†, M. S. Kandari† and V. M. Choubey‡ †Department of Physics, H.N.B. Garhwal University Campus Tehri Garhwal-249 001, India. ‡Wadia Institute of Himalayan Geology, Dehradun-248001, India Received June 12 1997, Amended August 26 1997, Accepted September 9 1997 Abstract — The results are presented of 83 measurements of radon (222Rn) in drinking water in Garhwal Himalaya, Northern India. The results are compared with international recommendations and some of the values are found higher than the recommended value of 400 Bq.l−1. The distribution pattern of radon in the drinking water and indoor air of the area has been obtained and is discussed in detail. Measurements of 222Rn levels in indoor air in the area have also been made. The results obtained are briefly discussed and some radon-rich areas are also identified.
INTRODUCTION Natural water usually contains dissolved radon due to omnipresent uranium in soil and rocks. Sometimes water contains a naturally elevated concentration of radon which can be released from the water into the ambient air, thus increasing the airborne radon concentration (1). Radon in water may therefore present dual pathways of exposure for individuals, through ingestion of water by drinking and through inhalation of air containing radon released from solution in water (2). It is therefore desirable to measure the radon in drinking water, especially when present in high concentrations. The results are presented of measurements of the radon in the drinking water of Garhwal Himalaya, Northern India. The water samples were taken from the springs used directly for drinking water. The water is usually transferred to houses directly from springs through pipelines without a storage tank. Sometimes people also collect the water from the spring and store it inside a room in big containers. Therefore, a small amount of radon decays in the process of transfer of radon from source to the room. Efforts were made to select the springs being used by a large population. The water samples were collected in a large grid (90 km ⫻ 110 km) with a distance of about 10 km between samples.
with the air and the resulting alpha activity was recorded. The calibration factor of 1 count.min−1 = 0.11 Bq.l−1 was used to convert the recorded alpha counts to Bq.l−1(3). Indoor
222
Rn
Measurement of indoor 222Rn levels was carried out by exposing small strips of LR-115 type II plastic track detector, affixed onto a glass slide; these were suspended inside the room to be monitored at a height of about 2 m from the ground floor. After an exposure period of 3 months, the detectors were retrieved. This exposure cycle was extended on a time integrated four quarterly cycle to cover all the four seasons of a calendar year to evaluate the annual indoor 222Rn levels. The exposed detectors were etched in 2.5 N NaOH solution Pump
Radon Detector cell Ca Cl2
METHODS OF MEASUREMENTS Spring water The apparatus used for the measurement of radon in drinking water is shown in Figure 1. A radon tight reagent bottle of 1 litre capacity holds 750 ml water and was connected in a closed circuit with a ZnS coated detection chamber through a hand operated rubber pump and a glass tube containing CaCl2 to absorb any moisture. The air was circulated in a closed circuit for a period of 10 min until the radon formed a uniform mixture 103
Phototube
Counting system
Figure 1. Apparatus for the measurement of radon in water.
R. C. RAMOLA, R. B. S. RAWAT, M. S. KANDARI and V. M. CHOUBEY
for 2 h at a constant temperature of 60°C and then scanned under an optical microscope for track density measurements. Measured track densities were then converted to the actual daughter activity concentration using a calibration curve generated in the laboratory by carrying out control experiments (4). From the daughter concentrations, the 222Rn gas concentrations were evaluated using an assumed equilibrium factor of 0.45 (5). The sensitivity factor obtained for the dosimetric configurations used in these sets of measurements was estimated to be 3.12 tracks.cm−2 per Bq.m−3 of 222Rn gas (6).
the room air is needed for calculating the total dose due to inhalation and ingestion of radon. The indoor radon levels were measured in the district and the measured annual average indoor 222Rn level was found to vary from 59 Bq.m−3 to 212 Bq.m−3 with a mean value of 109.6 Bq.m−3 (Table 2). These measured values are comparable with the variations in the country-wide 222 Rn concentration of 11 to 124.3 Bq.m−3(9). The houses surveyed are located in the hilly region of Garhwal Himalaya which consists of rock with a slightly higher uranium content. This area also lies between the Main Boundary Thrust (MBT) and Main
Table 1. Radon concentration in drinking water of Garhwal Himalaya. Observed radon concentration (Bq.m−3) Less than 20 20–50 50–100 100–200 More than 200
Number of values
47 23 5 6 2
0 100 200 300 400 500 600 700 800
The recorded values of radon in drinking water are given in Table 1. About 16% are seen to be higher than 50 Bq.l−1, while two of them exceed the international recommended limit of 400 Bq.l−1 as proposed by the Environmental Protection Agency, USA (7). The highest value (880 Bq.l−1) was found in the drinking water of Budhakedar. However, at another place in Budhakedar a low value was recorded (27 Bq.l−1), at a spot about 2 km from the high-value location. This lower value is due to the decay of radon before water reaches the sample collection site. The water sample was collected at about 100 m away from the spring, which is located on the hill and flows downhill before reaching the sampling site. In the process of transfer, radon emanates into the air and thus decreases the radon concentration in the water. Our recent study on environment radon at some places in Garhwal Himalaya shows that radon concentration is high in mud houses (8) and most of the houses in this area are mud houses. In view of the estimate that radon at 400 Bq.l−1 in water could lead to 0.15 Bq.l−1 in air (1), it appeared desirable to monitor radon in the indoor atmosphere of the study area. The distribution pattern of radon in the drinking water is shown in Figure 2. It shows that radon is distributed uniformly over the area studied except for a particular area where most of the values recorded were over 50 Bq.l−1. It is therefore important to initiate further studies in that area in order to determine the health hazard for the people living there. Since radon measurements in water do not directly indicate the dose to lung, the measurement of radon in
Radon concentration (pCi.l–1)
RESULTS AND CONCLUSIONS
10
0
80
80
Dis 60 tan c
4 e( 0 km )
20 0
20 0
40 ce tan Dis
60 ) (km
Figure 2. Distribution pattern of radon in drinking water of Garhwal Himalaya.
Table 2. Recorded average indoor radon concentration for different seasons at different places in Tehri Garhwal. Place
Number of house
Average radon concentration (Bq.m−3) Winter Summer Rainy Autumn Annual
Tehri New Tehri Padiyargaon Nail Malideval Koti Colony Manjur Dikholgaon Thanegaon Serain Rajgaon Uppu Dang Chamma Chham
104
12 10 11 11 3 5 4 3 2 2 5 5 4 3 2
148 126 233 170 197 135 82 87 77 91 136 55 57 65 130
93 135 210 126 110 81 68 69 59 91 117 51 51 63 118
109 135 215 137 133 130 87 94 77 90 137 — 72 69 116
139 143 190 139 150 110 74 102 63 118 — 72 60 81 114
122 135 212 143 148 114 78 88 69 98 130 59 60 70 120
MEASUREMENT OF RADON IN DRINKING WATER AND INDOOR AIR
Central Thrust (MCT) which may also contribute to observing higher indoor 222Rn levels. In general, indoor 222 Rn levels were higher in winter which may be due to poor ventilation of the houses. However, in some dwellings higher indoor 222Rn levels were recorded than the winter value as these houses were closed for a long time in summer. Our recent study on environmental radon at some places in Garhwal Himalaya shows that radon concentration is high in mud houses (8) and most of the houses in this area are mud houses. It has already been reported that the soil of a particular area is responsible for high radon concentrations in dwellings of the area. It was observed that radon concentration in spring water and indoor air were found to be higher in a parti-
cular area (Bhilangana Valley of Garhwal Himalaya). Based on the available data it may be concluded that the radon level in Garhwal Himalaya is higher than the normal level but well within the safe limit, except for a few places. Some radon-rich areas are identified and a detailed study is needed to estimate the health risk to the people living there. ACKNOWLEDGEMENTS Two authors (R.C.R. and R.B.S.R) are grateful to B.R.N.S., D.A.E. for providing financial support under the research scheme No. 27/4/93-G. One author (V.M.C.) is also grateful to the director, W.I.H.G., for providing the necessary facilities to carry out this investigation.
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