Radiation hazard indices of soil and water samples in ...

Applied Radiation and Isotopes 70 (2012) 2652–2660

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Radiation hazard indices of soil and water samples in Northern Malaysian Peninsula B.A. Almayahi n, A.A. Tajuddin, M.S. Jaafar School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia

H I G H L I G H T S c c c

For calculated and measured g_dose, R ¼ 0.88. R ¼ 0.81 for 222Rn and 226Ra. Hex and Hin o 1.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 22 April 2012 Received in revised form 23 July 2012 Accepted 24 July 2012 Available online 4 August 2012

The radioactivity quantity and quality were determined in soil and water samples in Northern Malaysian Peninsula (NMP) using HPGe spectroscopy and GR-135 spectrometer. The 226Ra, 232Th and 40 K concentrations in soil samples are 577 2, 687 4 and 427 717 Bq kg 1, respectively, whereas in water samples were found to be 2.86 7 0.79, 3.78 7 1.73 and 152 7 12 Bq l 1, respectively. These concentrations are within those reported from literature in other countries in the world. The radiological hazard indices of the samples were also calculated. The mean values obtained from soil samples are 186 Bq kg 1, 88 nGy h 1, 108 mSv y 1, 0.50 and 0.65 for Radium Equivalent Activity (Raeq), Absorbed Dose Rates (DR), Annual Effective Dose Rates (ED), External Hazard Index (Hex) and Internal Hazard Index (Hin) respectively, whereas, for water samples were found to be 20, 10, 13, 0.05 and 0.06, respectively. All the health hazard indices are well below their recommended limits, except in two soil sampling sites which were found to be n025 (1.1 Hex) and n026 (1.1 Hex, 1.6 Hin). The calculated and the measured gamma dose rates had a good correlation coefficient, R ¼0.88. Moreover, the average value radon is 20 (in the range of 7–64) Bq m 3, a positive correlation (R¼ 0.81) was observed between the 222 Rn and 226Ra concentrations in samples measured by the SNC continuous radon monitor (model 1029, Sun Nuclear Corporation) and HPGe detector, respectively. Some soils in this study with Hin and Hex o 1 are suitable for use in agriculture and as building materials. Also, in this study Hin and Hex o 1 for water samples, therefore, water after processing and filtration is safe and suitable for use in household and industrial purposes. & 2012 Elsevier Ltd. All rights reserved.

Keywords: Radiological hazard index Environmental radionuclides Water Soil Radon

1. Introduction The functioning of the Earth’s terrestrial systems is continuously affecting man and induced global changes. This is reflected by changes in the ecological functions of terrestrial systems such as surface water bodies (flood prevention), soils (fertility for food production) and groundwater (drinking water supply) (Froehlich, 2010). Contamination of land and water can occur from deposition of waste material originally introduced into the atmosphere, from discharge directly into surface or subsurface waters, from wastes

n

Corresponding author. Tel.: þ60 172 431 529. E-mail addresses: [email protected], [email protected] (B.A. Almayahi). 0969-8043/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2012.07.021

placed in or on the ground. The primary reason for being concerned about radioactive contamination of the environment is that it may result in exposure of humans. Ground contaminants may eventually be mobilized by groundwater or erosion surface waters are coupled to subsurface aquifers, soils, and the atmosphere. Atmospheric pollutants eventually deposit on soils or surface waters and the mechanisms for removal of contaminants from soil involve transport by water by a sequence of processes, including surface runoff and leaching into soil water that eventually seeps to streams. People live surrounded by natural radioactivity. There are radioactive isotopes in our bodies, houses, air, water and ground (Eisenbud and Gesell, 1997; Henriksen and Maillie, 2003). Natural environmental radioactivity due to gamma radiation depends on the geological and geographical conditions, and found in various quantities in soils around the world (UNSCEAR, 2000). Naturally occurring unstable radioactive elements are found in all rocks,

B.A. Almayahi et al. / Applied Radiation and Isotopes 70 (2012) 2652–2660

soils, and water. The common long-lived radioactive elements, U and Th, decay slowly to produce other radioactive elements, such as Ra, which undergo radioactive decay. 226Ra is moderately soluble in water and can enter ground water by dissolution of aquifer materials, desorption from rock or sediment surfaces, and ejection from minerals by radioactive decay. 226Ra decays with alpha emission to the inert gas 222Rn (T1/2 ¼3.8 d). Radon is a naturally occurring form of radiation that permeates the Earth’s atmosphere. 222Rn is able to seep through water, soil surfaces, and structural barriers. Levels of 222Rn gas concentration can vary by geological and geographical locations. Statistics by the U.S. Surgeon General’s Office list radon gas poisoning as the second leading cause of lung cancer in USA. Radionuclides concentrations of water and soil are good indicators of the levels of pollution. In this study, we have reported the 226Ra, 232Th and 40K activities obtained from soils and water in NMP. 1.1. Study area Peninsula Malaysia is situated between latitudes 01N and 71N and longitudes 1001E and 1051E within the equatorial region of Southeast Asia and the maritime continent, its total annual rainfall of 300 cm is high. Records of reports from the Global Extreme Flood Events by the Dartmouth Flood Observatory affirm that extreme heavy rainfalls over Malaysia, Indonesia and southern Thailand are unusual during the winter monsoon (Dartmouth Flood Observatory, 2003). Malaysian floods are the dominant risks followed by forest risks, tsunamis, cyclonic storms, landslides and earthquakes. The wide spread floods took place along the western coast of the Malay Peninsula, extending from the states of Penang, Perlis, Kedah, and Perak in Northern Malaysian Peninsula (NMP). Table 1 shows geographic site of sampling points and the geology of the study area is shown in Fig. 1 (Director General of Geological Survey, 1985).

2. Materials and methods

2653

wherever access was possible for road throughout NMP, taking into account that soils are not mixed with soils from other sites (original soil). Precautions against accidental mixing of samples for the different sites were considered very important during the collection and transport of soils. Soils samples were collected at different range positions 0 cm to 10 cm, 10 cm to 20 cm, 30 cm to 40 cm, and 40 cm to 50 cm, with an 18 cm diameter using an Earth Auger Drill (DZ500). A total of (48) soil samples were dried at 110 1C for 1 day in an oven (Memmert, Germany) to ensure complete removal of moisture. Dried samples were grinded using large pestle and mortar of 25.6 cm diameter (ceramic, England) and sifted through a 1 mm sieve. Each sample was weighed and sealed using standard electric tape in standard Marinelli beaker. The samples were stored for a period of about 1 month before counting to achieve equilibrium for 238U and 232Th with their respective progeny (Myrick et al., 1983). A total of (16) water samples (500 ml) were collected using plastic bottles from sea, river, rain, and waterfall in these areas as shown in Table 1. Marinelli beakers of 500 ml capacity were washed with dilute hydrochloric acid, rinsed with distilled water, dried for avoid contamination, and filled with known volumes (400 ml) of the water samples. The beakers were sealed and left for 1 month to reach radioactive secular equilibrium. The water beaker was shook for (30 s) to homogenize distribution of radionuclides into the beaker before radiometric analysis. The water was then tested on HPGe detector for counting. In HPGe spectroscopy measurements of gamma emitters were conducted without the need for chemical treatment. The radionuclides concentration was determined from the photopeaks of (214Pb (295 keV), 214Bi (609 keV)) of 226Ra and the photopeaks of (212Pb (238 keV), 208Tl (583 keV), 228Ac (969 keV)) of 232Th, while 40 K was determined from the photopeak of 1460.8 keV. These peaks had been chosen to include whole spectrum for the reduction of the error ratio, and for appropriate statistical data using different energies.

2.1. Sample collection and preparation 2.2. Survey instruments Soil samples were collected from areas of different soil types in 12 sampling sites in NMP, with four samples collected from each site. Selection and sampling aimed at including the entire NMP,

Gamma dose measurement was conducted using a fully portable handheld (3.8 cm 5.5 cm) spectrometer NaI (Tl) detector

Table 1 Geographic site of sampling points. Sc *

011 002 058 * 069 * 088 * 091 * 110 * 015 * 016 * 171 * 182 * 196 * 201 * 211 * 229 * 233 * 245 * 259 * 266 * 276 * *

Sampling site Batu Uban, Penang G. Sanggul, Penang Balik Pulau, Penang Bukit Dumbar, Penang Kg. Batu Feringhi, Penang Teluk Bahang, Penang Penang Hill, Penang Kg. Pulau Chengai, Kedah Kg. Lubok Peringgi, Kedah Kg. Rama, Perlis Bukit Ayer Kangar, Perlis, Malaysia–Thailand border Forest Research Complex, Perlis, Malaysia–Thailand border Kg. Alor Radis, Perlis Kg. Telaga Baru, Kedah Kg. Baru Padang Sanai, Kedah Pulai Kedah, Kedah Lebuh Raya Grik, Perak Kg. Bukit Sapi, Lenggong, Perak Kg. Batu Enam, Perak Kg. Titi Teras, Kedah

Sc-Sites code, asl-above mean sea level.

Latitude (N)

Longitude (E)

0

0

05122 28.8* 051160 50.0* 051200 17.5* 051230 19.1* 051280 01.1* 051270 41.0* 051250 31.3* 051490 57.60* 06170 43.20* 06118’18.60* 061320 47.10* 061390 15.40* 061240 51.00* 061210 4.70* 061190 58.50* 051390 26.80* 051270 55.90* 051090 3.50* 041220 49.30* 051500 37.20*

100118 56.8* 1001110 49.4* 1001110 45.7* 1001190 10.7* 1001150 04.6* 1001120 15.5* 1001160 09.6* 1001290 10.10* 1001210 54.00* 1001120 23.80* 1001100 6.80* 1001140 30.60* 1001130 32.70* 1001210 21.20* 1001460 36.00* 1001530 31.20* 101150 3.10* 101140 17.80* 101130 23.80* 1001270 58.80*

Error (m)

asl (m)

73 73 73 74 75 77 75 73 74 74 75 74 76 74 74 75 75 73 74 76

53 15 14 14 46 29 738 27 12 17 59 90 13 17 40 52 196 142 29 15

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Fig. 1. A geological map of NMP (Director General of Geological Survey, 1985) depicting the area of this study.

with (12.7 mm 50 mm) Geiger–Muller tube (Model GR-135, Exploranium, Canada). The instrument had almost flat energy response to gamma radiation between 40 keV to 1.2 MeV (Knoll and Glein, 1989). The identifier offers options to measure the absorbed dose rate and to identify the radioactive nuclides present automatically. The measurement range of the tubes for 137Cs is between

10 nSv h 1 to 10 mSv h 1. All logged data are time-stamped and stored for later analysis using a PC and the IdentiVIEW software. In addition, the software includes a 1024 channel high-resolution analyser; a stabilized, thermally corrected gain; and pulse pile-up rejection to reduce errors at high-count rates. The total gamma ray exposure rates from the soil were measured in 5 min at 3 readings per site, and spectrum analysis was


2.3. Gamma-ray spectrometry and calibration Naturally occurring radionuclides concentrations were measured from the soil and water samples using a High Purity Germanium (HPGe) detector. The HPGe detector had an energy resolution of 1.85 keV (FWHM) for the 1332.5 keV gamma-ray transition of 60Co source. A constant counting time for calibration sources 241Am, 137Cs, 60 Co, and 152Eu (of activities of 331 kBq, 372 kBq, 387 kBq, and 383 kBq, respectively) from the International Atomic Energy Agency, set no. 34 (8 radioactive sources), for the background spectrum, and for measuring soil and water samples of 36,000 s and 86,400 s, respectively was adopted. Instrument calibration was done at multiple energies from 59.54 keV to 1408.30 keV,

and Fig. 2 shows typical soil spectrum after the calibration. The absolute detection efficiency of the HPGe detector was determined using 241Am, 226Ra, 133Ba, 137Cs, 22Na, 60Co, and 152Eu sources. The absolute efficiency of the HPGe detector for gammaray energy was calculated from the formula

e¼

n

ð1Þ

lt d

tP g ðEÞNeo

where n is the net area under the full energy peak, E is gamma energy, t is the counting time, Pg (E) is the gamma emission probability at energy E, No is the activity of the source (Becquerel), l is the decay constant¼ln 2/T1/2. T1/2 is the half-life of the radionuclides, and td is the decay time. The efficiency calibration curve for the HPGe detector is shown in Fig. 3. The background gamma-ray spectrum of the detection system was determined with an empty Marinelli beaker with the same geometrical conditions as the soil and water samples, and was stripped from the spectra of each sample. The activity of each sample was determined using MAESTRO software with 16,384 channels, enables data acquisition, storage, and display of the acquired spectra. The system also contains the electronic components of amplifier and power supply. The HPGe is surrounded by a lead shielding 5 cm in thickness, 9.5 cm in diameter, and 20 cm in height to

0.025 Absolute Efficiency

conducted for 3600 s at a level of 1 m above the ground level in the sites. The GR-135 system was calibrated against a 137Cs standard with FWHM¼7% and checked daily for stability using a low-activity 0.25 mCi 137Cs source. The NaI (Tl) detector is the most widely used device for all kinds of gamma ray surveys due to its efficiency (IAEA, 1979). The radon concentration at a level of 1 m above the soil sampling sites was measured in Bq m 3 for 3600 s using a portable continuous radon monitor (SNC, model 1029). The SNC monitor is a patented electronic detection device made for the measurement of radon gas concentration by 218Po (6 MeV) using a diffused-junction photodiode sensor (SNC, 2010). This model 1029 also includes monitoring of temperature, humidity, and barometric pressure. The SNC monitor can be connected to a computer and a thermal printer using a USB cable. The windows software version 2.2 on the provided CD can be used to download measurements. The radon monitor software can be used to send basic parameters to the radon monitor, although this can also be done using the keypad on the radon monitor. The SNC detector had been factory-calibrated, with a working range of 1 Bq m 3 to 99,990 Bq m 3 and its sensitivity is 0.6 counts per hour per Becquerel per cubic meter (c h 1 Bq m 3), with size and weight of 236 122 74 mm3 and 0.91 kg, respectively. Global Positioning System (GPS) Garmin model 60 CSX (Garmin International, Inc., 2007) with accuracy of less than 10 m was used to determine the coordinates of the sampling sites.

2655

0.020 0.015 0.010 0.005 0.000 0

200

400

600 800 1000 1200 1400 1600 Energy (keV)

Fig. 3. The efficiency calibration curve for the HPGe detector (Almayahi et al., 2012).

Fig. 2. Typical spectrum after calibration with stripped the background.

2656


reduce the gamma ray background (Tsoulfanidis, 1995). The specific activity is defined as follows: Specific activity ðBq kg

1

Þ¼

Net AreaB:G t eP g M

Table 3 Activity concentrations of natural radionuclides (Bq kg 1) in soil samples (0–50) cm.

ð2Þ

Sc

where Net Area ¼Net area under energy peak (count). B.G¼the number of counts for the background spectrum, e ¼the absolute efficiency of the detector, and M¼the weight of the dried sample (kg).

*

015 016 017 * 018 * 019 * 020 * 021 * 022 * 023 * 024 * 025 * 026 Total * *

2.4. Radiological hazard index The values calculated for radiological hazard index for soil and water samples are shown in Tables 4 and 5. 2.4.1. Radium equivalent activity (Raeq): The significance of 226Ra, 232Th, and 40K concentrations, with respect to radiation exposure, was defined in terms of radium

Table 2 Specific activity (Bq kg 1) of

214

Pb,

214

Bi,

228

Ac,

212

Sc

D (cm)

214

*

015

*

016

*

017

*

018

*

019

*

020

*

021

*

022

*

023

*

024

*

025

*

026

0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50 0–10 10–20 30–40 40–50

13.7 7 4.3 15.0 7 1.3 46.3 7 2.8 83.0 7 2.8 92.6 7 5.0 93.6 7 3.3 76.4 7 3.3 79.2 7 3.2 18.6 7 1.4 15.6 7 1.4 46.8 7 2.7 51.0 7 2.6 34.0 7 2.3 32.8 7 2.3 27.5 7 2.3 29.3 7 2.3 30.5 7 1.8 27.2 7 1.9 28.2 7 1.8 29.5 7 1.7 17.3 7 1.6 16.6 7 1.3 55.4 7 2.9 56.1 7 2.9 43.0 7 1.8 41 7 1.2 36.4 7 2.3 40.4 7 1.9 5.8 7 0.7 4.44 7 0.6 31.4 7 1.6 31.7 7 1.6 50.4 7 2.2 51.2 7 2.2 86.7 7 3.0 88.6 7 3.0 54.2 7 2.6 45.0 7 2.1 52.6 7 2.4 50.3 7 2.3 38.6 7 1.9 33.8 7 1.9 120 7 3.3 131.0 7 3.6 160 7 3.9 159 7 3.7 239 7 4.4 240.6 7 4.6

D-Depth.

Pb

Pb,

208

Tl, and 214

40

226

232

Ra

40

Th

K

Avg.

Range

Avg.

Range

Avg.

Range

33 7 2 79 7 3 35 7 2 29 7 2 26 7 1 43 7 2 35 7 2 17 7 1 63 7 2 49 7 2 87 7 2 185 7 4 57 7 2

20–46 73–86 21–49 27–30 22–29 22–57 35–37 7–29 47–84 42–54 53–121 151–222 7–222

817 3 977 4 597 3 597 3 427 2 467 3 547 11 257 1 437 3 637 3 1057 3 138 7 4 687 3

53–121 83–106 38–79 53–65 34–48 36–53 47–62 10–40 33–60 58–67 61–146 119–158 10–158

270 7 14 602 7 21 644 7 21 772 7 23 279 7 14 231 7 17 214 7 14 137 7 8 205 7 13 183 7 14 1165 7 28 417 7 20 427 7 17

104–423 570–635 633–659 693–844 227–319 142–305 154–287 129–151 158–274 132–225 1102–1225 387–454 104–1225

K.

Bi

27.8 71.6 26.2 71.6 43.2 72.1 44.8 73.1 75.4 72.8 79.9 72.6 69.5 72.5 67.9 72.6 33.3 71.7 26.4 71.7 45.0 72.0 46.9 72.1 27.6 71.9 28.0 71.9 26.7 71.8 30.4 71.6 29.1 71.3 28.4 71.4 20.0 70.9 27.5 71.3 27.9 71.9 26.8 71.6 59.1 72.1 55.2 72.3 28.3 71.6 28.3 71.6 31.0 71.2 33.4 71.8 10.1 70.8 9.0 70.7 23.2 71.4 26.7 71.3 44.6 71.7 43.4 71.8 77.4 72.4 79.7 72.3 54.6 72.0 52.8 72.1 43.7 71.9 42.2 72.2 68.6 72.3 73.1 72.3 109.0 72.8 112.0 73.0 142 73.2 139 73.2 206.3 73.7 201.8 73.7

228

Ac

88.6 7 6.0 91.0 7 6.2 112.1 7 9.0 141.3 7 7.7 126.4 7 9.1 131.5 7 8.6 101.3 7 9.1 109.1 7 8.9 46.4 7 5.7 62.2 7 5.7 93.5 7 7.6 97.8 7 7.5 74.7 7 8.0 68.4 7 8.3 62.7 7 7.2 68.3 7 6.6 62.5 7 4.3 63.6 7 4.2 48.7 7 5.0 50.1 7 5.2 63.2 7 5.5 55.0 7 5.5 51.6 7 8.6 49.5 7 8.8 61.9 7 4.9 55 7 4.1 67.1 7 6.7 77.7 7 5.7 15.0 7 2.6 16.0 7 2.7 42.4 7 5.3 48.1 7 4.8 76.3 7 6.3 72.9 7 6.3 105.5 7 9.4 131.1 7 8.0 70.3 7 7.3 77.1 7 6.9 73.8 7 6.5 82.4 7 5.4 87.8 7 6.7 101.7 7 6.7 164.5 7 10 157.2 7 10 135 7 10.2 140 7 9.6 150 7 8 177.2 7 10

212

Pb

49.3 7 1.2 43.0 7 1.0 120 7 1.0 140.0 7 1.9 139 7 2.0 145.4 7 2.0 114.3 7 2.0 146.4 7 2.6 43.0 7 1.1 39.0 7 1.1 907 1.0 106.2 7 1.7 95.6 7 1.5 93.3 7 1.6 73.7 7 1.6 82.0 7 2.0 63.6 7 1.1 61.8 7 1.1 59.8 7 1.2 65.5 7 1.1 30.07 1.1 31.0 7 1.1 707 1.5 79.0 7 1.6 64.0 7 0.2 61.6 7 1.2 85.7 7 1.6 78.9 7 1.6 11.5 7 0.5 10.5 7 0.4 53.8 7 1.1 56.5 7 1.1 95.9 7 1.4 91.9 7 1.4 120 7 1.4 162.1 7 1.9 89.7 7 1.6 94.3 7 1.5 84.6 7 1.4 88.2 7 1.4 62.6 7 1.3 59.0 7 1.0 190.0 7 2.0 216.6 7 2.2 172 7 2.1 169 7 2.1 2007 2.5 230.0 7 2.5

208

Tl

22.4 7 1.1 26.4 7 1.0 45.2 7 1.3 40.07 1.2 45.3 7 1.4 42.5 7 1.5 35.4 7 1.4 33.1 7 1.5 25.2 7 1.0 21.5 7 1.0 307 1.0 35.3 7 1.8 26.6 7 1.2 27.0 7 1.1 20.07 1.0 24.4 7 1.1 19.0 7 0.8 19.6 7 0.8 19.9 7 0.8 20.5 7 0.8 16.5 7 0.9 18.7 7 0.9 21 7 1.1 25.7 7 1.2 17.6 7 0.9 11 7 0.5 20.07 2.1 30.3 7 2.7 6.4 7 0.4 5.5 7 0.4 16 7 0.6 17.8 7 0.8 27.5 7 1.0 22.5 7 0.8 39.0 7 0.8 49.7 7 1.3 28.8 7 1.0 29.0 7 1.0 27.1 7 1.0 25.1 7 1.0 35.0 7 1.14 30.07 1.0 407 1.1 66.4 7 1.5 50.2 7 1.5 40.07 1.3 61.0 7 1.6 67.9 7 1.8

40

K

1047 10 135 7 12 413 7 17 423 7 17 613 7 22 635 7 21 582 7 21 571 7 21 659 7 22 6007 20 599 7 19 659 7 21 844 7 24 7507 23 6507 18 693 7 24 228 7 11 212 7 13 268 7 13 289 7 12 3057 17 319 7 17 247 7 20 268 7 19 159 7 12 155 7 12 262 7 17 287 7 15 132 7 7.8 129 7 7.8 1407 9.8 151 7 8.4 159 7 10 1607 9.9 246 7 17 274 7 15 226 7 14 219 7 15 225 7 15 163 7 13 1156 7 28 11507 27 12007 28 1225 7 27 454 7 21 438 7 22 3507 18 395 7 19


equivalent activity (Raeq) in Bq kg 1. Raeq was calculated from Eq. (3) (Beretka and Matthew, 1985): Raeq ¼ C Ra þ1:43C Th þ 0:077C K

ð3Þ

where CRa, CTh and CK are the activity concentrations of 226Ra, 232 Th and 40K in Bq kg 1, respectively. This equation is based on the estimate that 1 Bq kg 1 of 226Ra, 0.7 Bq kg 1 of 232Th and 13 Bq kg 1 of 40K generate the same gamma-ray dose rate (Stranden, 1976; Malanca et al., 1993; Iqbal et al., 2000; Siak et al., 2009). The maximum value of Raeq must be less than 370 Bq kg 1 for safe use as recommended by the Organization for Economic Cooperation and Development (OECD, 1979).

700 Bq kg 1 for 40K (UNSCEAR, 2000). From Table 4, the higher Ra and 232Th concentrations in water samples are noted in samples n058 (Balik Pulau, Penang) and n069 (Bukit Dumbar, Penang), respectively, and the higher 40K concentration noted in sample n019 in Forest Research Complex, Perlis, Malaysia– Thailand border, whereas the lower 226Ra and 232Th concentrations are noted in sample n021 in Kg. Telaga Baru, Kedah, and the 226

Table 4 Activity concentrations of natural radionuclides (Bq l 1) in water samples from NMP. Sc

Water type

226

*

Sea Sea Sea Sea Waterfall Sea Rain Rain Rain Waterfall Rain River River River Rain River

2.88 7 0.48 2.33 7 1.16 7.037 1.38 2.34 7 1.02 0.877 0.30 2.71 7 0.63 3.067 0.49 2.93 7 0.48 5.93 7 1.24 3.13 7 0.95 0.947 0.70 1.98 7 0.30 0.707 0.64 3.44 7 1.31 1.83 7 0.51 3.73 7 1.02 2.867 0.79

011 002 * 058 * 069 * 088 * 091 * 110 * 015 * 017 * 018 * 019 * 020 * 021 * 022 * 024 * 027 Avg. *

2.4.2. Air-absorbed dose rates The absorbed dose rates in outdoor air, DR (nGy h 1), at about 1 m above the surface of the ground were calculated using Eq. (4) (UNSCEAR, 2000): DR ¼ 0:462C Ra þ 0:621C Th þ0:041C K

ð4Þ

2.4.3. Annual outdoor effective dose equivalent To estimate the annual outdoor effective doses (ED), the conversion coefficient from absorbed dose rate in air to effective dose (0.7 Sv Gy 1) and the outdoor occupancy factor (0.2) are used (UNSCEAR, 2000). The effective dose equivalent rate, in units of mSv yr 1, is calculated from Eq. (5): ED ¼ DR 8766 h yr1 0:7ðSv Gy1 Þ 0:2 103 where DR is the absorbed dose rates in air (nGy h

1

40

Th

K

1.96 70.90 2.18 72.87 3.80 73.56 8.64 71.46 2.09 71.57 1.58 71.37 3.69 70.89 4.23 71.12 4.25 72.22 5.52 71.8 4.27 71.29 1.59 71.57 0.55 70.23 5.59 72.12 2.61 71.43 8.03 73.37 3.78 71.73

190 713 220 719 190 717 150 715 127 712 201 712 177 712 84 77 204 717 146 715 222 713 74 77 171 710 124 717 53 75 105 712 152 712

Table 5 Radiation hazard indices of soil samples of NMP.

).

ð6Þ

2.4.5. Internal hazard index (Hin) Internal hazard index (Hin) is given by Eq. (7) (Beretka and Matthew, 1985): Hin ¼ C Ra =185 þ C Th =259 þ C K =4810

232

Ra

ð5Þ

2.4.4. External hazard index (Hex) Radiation exposure due to 226Ra, 232Th and 40K may be external. This hazard, defined in terms of external or outdoor radiation hazard index and denoted by Hex, can be calculated using Eq. (6) (Beretka and Matthew, 1985): Hex ¼ C Ra =370 þC Th =259 þC K =4810 4 1

2657

ð7Þ

Hin must be less than one for safe use of samples and for the radiation hazard to be negligible.

3. Results and discussion The results of radionuclides concentrations of the soil and water samples are presented in Tables 2–4. Soil 226Ra, 232Th and 40 K were found to be 5772, 6874 and 427717 Bq kg 1, respectively. For water samples, the corresponding values were found to be 2.8670.79, 3.7871.73, and 152712 Bq kg 1, respectively. From Table 3, the higher 226Ra and 232Th concentrations in soil samples are noted in sample n026 in Kg. Batu Enam, Perak, and the higher 40K concentration noted in sample n025 in Lenggong, Perak, whereas the lower 226Ra, 232Th, and 40K concentrations are noted in sample n022 in Kg. Baru Padang Sanai, Kedah. World average concentrations are 35 Bq kg 1 and 45 Bq kg 1 for 226Ra and 232Th, respectively; and typical ranges are 16–116 Bq kg 1 for 226 Ra and 7–50 Bq kg 1 for 232Th. The world average concentration is 420 Bq kg 1 for 40K, and the typical range is 100–

Sc

Raeq (Bq kg 1)

DR (nGy h 1)

ED (lSv y 1)

Hex

Hin

*

169.6 264.0 168.9 172.8 107.5 126.5 128.6 63.2 140.2 153.1 326.8 414.4 186

79.6 124.2 81.9 84.8 51.0 58.9 60.1 29.8 64.3 70.7 157.1 188.8 88

97.7 152.4 100.5 104.1 62.6 72.3 73.7 36.5 78.9 86.8 192.8 231.7 108

0.45 0.71 0.45 0.46 0.29 0.34 0.34 0.17 0.37 0.41 0.88 1.11 0.50

0.54 0.92 0.55 0.54 0.36 0.45 0.44 0.21 0.54 0.54 1.11 1.61 0.65

015 016 * 017 * 018 * 019 * 020 * 021 * 022 * 023 * 024 * 025 * 026 Avg. *

Table 6 Radiation hazard indices of water samples of NMP. Sc

Raeq (Bq kg-1)

DR (nGy h-1)

ED (lSv y 1)

Hex

Hin

*

20.3 22.3 27.0 26.2 13.6 20.4 21.9 15.4 27.7 22.2 24.1 9.9 14.5 20.9 19.8 9.9 20

10.7 11.9 13.7 13.2 7.2 10.8 11.3 7.6 14.1 11.2 12.7 5.0 7.9 10.5 10.2 5.0 10

13.1 14.6 16.8 16.2 8.8 13.3 13.9 9.4 17.3 13.8 15.6 6.2 9.8 12.9 12.5 6.2 13

0.05 0.06 0.07 0.07 0.03 0.05 0.05 0.04 0.07 0.06 0.06 0.02 0.03 0.05 0.05 0.02 0.05

0.06 0.06 0.09 0.07 0.03 0.06 0.06 0.04 0.09 0.06 0.06 0.03 0.04 0.06 0.06 0.03 0.06

011 002 * 058 * 069 * 088 * 091 * 110 * 015 * 017 * 018 * 019 * 020 * 021 * 022 * 024 * 027 Avg. *

2658


lower 40K concentration noted in sample n024 in Lebuh Raya Grik, Perak. The average value of Raeq is 186 Bq kg 1 and 20 Bq kg 1 for soil and water, respectively as shown in Tables 5 and 6, which are less than the 370 Bq kg 1 and 49 Bq kg 1 recommended maximum levels of radium equivalents in soil and water, respectively.

Table 7 Typical concentrations of K, U, Th, Rn and gamma-ray dose rate in-situ at 1 m above sampling sites using GR-135 spectrometer in NMP. Sc

40

K (Bq kg 1)

238

U (Bq kg 1)

232 Th (Bq kg 1)

DR (nGy h 1)

Radon (Bq m 3)

*

125 657 688 876 156 657 250 125 125 125 939 344 455

60 28 45 26 18 23 34 17 45 46 88 104 45

175 73 79 73 39 63 78 24 80 65 122 118 83

116 109 132 106 59 68 91 58 114 102 192 178 110

7.1 14.2 14.2 7.1 7.0 7.1 11.0 14.2 28.4 21.3 42.6 63.9 20

Calculated Dose Rate (nGy h-1)

200

R=0.88

1200

180

R=0.86 1000

160 140

40K(HPGe)

015 016 * 171 * 182 * 196 * 201 * 211 * 229 * 233 * 245 * 259 * 266 Avg. *

Therefore, the soil and water are suitable for use for agriculture and building materials. Also, this water is suitable for use in residences as drinking water. The average absorbed dose rate is 88 (29.8–188.8) nGy h 1 and 10 (5.0–14.1) nGy h 1 for soil and water samples. This value agrees with the worldwide average concentrations of these radionuclides in soils of 92 nGy h 1 (UNSCEAR, 2000). The outdoor annual effective doses ranged from 36.5 mSv yr 1 to 231.7 mSv yr 1 with a mean value of 108.0 mSv yr 1 (0.1 mSv yr 1) in soils, while the worldwide average annual effective dose is 0.5 mSv yr 1 and the results for individual countries being generally within the 0.3 mSv yr 1 to 0.6 mSv yr 1 range (UNSCEAR, 2000) and the outdoor annual effective doses ranged from 6 mSv yr 1 to 17 mSv yr 1 with a mean value of 12 mSv yr 1 (0.01 mSv yr 1) in water. The calculated external hazard values are between 0.17 Hex to 1.11 Hex (mean¼ 0.50 Hex) and 0.02 Hex to 0.07 Hex (mean¼0.50 Hex) for soil and water samples, respectively. The value of Hin ranged from 0.21 Hin to 1.61 Hin (mean¼0.65 Hin) and 0.21 Hin to 1.61 Hin (mean¼ 0.65 Hin) for soil and water samples, respectively. The values of Hex in sampling site n026 and Hin of sampling sites n025 and n026 are higher than unity, which may cause harm to people in this region. Table 7 shows measured concentrations (40K, 238U, 232Th) and gamma-ray dose rate by using GR-135 spectrometer, where the average 40K, 238U and 232Th concentrations are 455 Bq kg 1,

120 100

800 600 400

80 200

60

0

40 20

40

60

80

100 120 140 160 180 200

0

200

400

Measured Dose Rate (nGy h-1) 200 180

800

1000

140 R=0.80 120

160 232Th(HPGe)

140 226Ra(HPGe)

600 40K(Gr-135)

120 100 80

R=0.65

100 80 60

60 40

40 20

20

0 20

40

60

80

238U(GR-135)

100

120

20

40

60

80

100

120

140

160

180

232Th(GR-135)

Fig. 4. Concentrations and dose rates for soil samples: (a) calculated versus measured dose rates, (b), (c), and (d) measured concentrations (K, U, Th, Ra) by a GR-135 and HPGe.


45 Bq kg 1 and 83 Bq kg 1, respectively and the measured dose rates ranged from 58 nGy h 1 to 192 nGy h 1. The calculated and measured dose rates using HPGe and GR-135, respectively from the soil samples of the present study had a good correlation coefficient R of 0.88, a good correlation coefficients R of 0.86 (40K), 0.80 (226Ra, 238U) and 0.65 (232Th), as shown in Fig. 4. A positive correlation was obtained between the radon and radium concentrations measured by the continuous radon

monitor SNC and HPGe detector, respectively, as shown in Fig. 5. Table 8 summarizes the natural radioactivity levels and radiation hazard indices in soils obtained in some world regions as well as this study. 226Ra values measured in this study are approximately compatible with values for Norway (Dowdall et al., ˇ 2003) and lower than that reported in Serbia (Zunic et al., 2007), Jordan (Al-Kharouf et al., 2008), Hungary (Papp et al., 2002), China (Song et al., 2012), and Malaysia (Almayahi et al., 2012) and higher than the values reported in other areas (UNSCEAR, 2000; Agbalagba and Onoja, 2011; Abd El-mageed et al., 2011; Alam et al., 1999; Ahmed and El-Arabi, 2005; Alias et al., 2008; Santawamaitre et al., 2011; Montes et al., 2012). Also, 232Th activity concentrations obtained in this study, tends to match that of values reported in Yemen (Abd El-mageed et al., 2011), and lower than that reported in China (Song et al., 2012), Malaysia (Almayahi et al., 2012) and higher than the values reported in other areas (UNSCEAR, 2000; Agbalagba and Onoja, 2011; ˇ Dowdall et al., 2003; Zunic et al., 2007; Al-Kharouf et al., 2008; Perrin et al., 2006; Papp et al., 2002; Alam et al., 1999; Ahmed and El-Arabi, 2005; Santawamaitre et al., 2011; Montes et al., 2012). Whereas, 40K values in the present study tends to match with values reported in France (Perrin et al., 2006), and lower than that reported in Yemen (Abd El-mageed et al., 2011), Egypt (Ahmed and El-Arabi, 2005), Malaysia (Almayahi et al., 2012) and China (Song et al., 2012), and higher than the values reported in other areas (UNSCEAR, 2000; Agbalagba and Onoja, 2011; ˇ Dowdall et al., 2003; Zunic et al., 2007; Al-Kharouf et al., 2008; Papp et al., 2002; Alam et al., 1999; Alias et al., 2008; Santawamaitre et al., 2011; Montes et al., 2012). Comparing the

222Rn

concentration (Bq m-3)

70 R= 0.81

60 50 40 30 20 10 0 0

20

40

60 226Ra

80

2659

100 120 140 160 180 200

concentration (Bq kg-1)

Fig. 5. Relation between radon and radium concentrations for soil sampling sites.

Table 8 Activity concentrations of natural radionuclides (Bq kg 1) and radiation hazard indices of soil samples of NMP using HPGe detector. Country

D (cm)

226

232

40

Nigeria (Agbalagba and Onoja, 2011) Norway (Dowdall et al., 2003) ˇ Serbia (Zunic et al., 2007)

10–15 0–12 20–50

17–29 17–137 24–1810

15–33 10–52 –

Jordan (Al–Kharouf et al., 2008) France (Perrin et al., 2006) Hungary (Papp et al., 2002) Yemen (Abd El-mageed et al., 2011) Bangladesh (Alam et al., 1999) Egypt (Ahmed and El-Arabi, 2005) Malaysia (Alias et al., 2008) Thailand (Santawamaitre et al., 2011) Argentina (Montes et al., 2012) China (Song et al., 2012) Malaysia (Almayahi et al., 2012) World (UNSCEAR, 2000) MalaysiaP

0–32 5–10 0–20 0–2 7.5 25 0–20 5 9,10 0–30 0–50 – 0–50

62–660 – 21–1256 16–84 10–27 8–17 10–42 54–65 30–57 11–604 64–799 17–60 7–222

18–25 22–42 15–41 18–113 27–49 3–16 – 60–69 35–48 22–701 16–667 11–64 10–158

Ra

Th

Raeq (Bq kg 1)

DR (nGy h 1)

ED (lSv y 1)

Hex

Hin

98–410 114–643 173–649

50–110 – –

23–52 – 92–316

64–29 – –

0.29–0.14 – –

0.18–0.37 – –

179–307 348–802 176–567 63–1664 117–688 838–1870 11–383 393–477 568–817 20–2097 87–1827 140–850 104–1225

12–702 – – 191 77–151 152 – – – 230–676 275–1154 – 63–414

45–71 – – 89 74–35 82 13–50 81–90 – 86–237 128–521 – 29–188

55–87 – – – – – – 100–110 – 110–290 471–2550 – 36–231

0.87–4 – – 0.52 – – 0.08–0.31 – – 0.6–1.8 0.74–3.11 – 0.17–1.1

– – – – – – – – – – 1.13–4.91 – 0.21–1.61

K

P-Present study.

Table 9 Activity concentrations of natural radionuclides (Bq l 1) and radiation hazard indices of water samples of NMP. Country

Water type

226

232

Nigeria (Agbalagba and Onoja, 2011) Yemen (Abd El-mageed et al., this issue)

Lake Ground Spring Drinking Lake Ground Sea Waterfall Rain River

12 3.5 3.48 ND 22.1 11.6 3.45 2.00 2.93 2.44 2.70

12 1.26 1.00 – 0.19 9.19 3.63 3.80 3.81 3.94 3.79

Jordan (Saqan et al., 2001) Sudan (Alfatih et al., 2008) MalaysiaP

Avg.

Ra

Th

40

DR (nGy h 1)

ED (lSv y 1)

Hex

Hin

97 17 16 24 – – 190 136 148 118 148

18 – – – – – 12.0 9.2 11.1 7.1 9.8

22 0.63 – – 3.79 186 14.8 11.3 13.7 8.7 12.1

0.077 – – – – – 0.050 0.045 0.054 0.030 0.044

0.132 – – – – – 0.06 0.045 0.062 0.040 0.051

K

2660


results of the present study, it is very important that the focus was on the depth of the soils obtained and the type of a detector used. The results tended to vary from one depth to another. Thus, the current work compared the results with those from other regions of the world for the same soil depth or close to the depth considered. Table 9 summarizes the natural radioactivity levels and radiation hazard indices for water obtained in some world regions and this study. 226Ra values measured in this study are approximately compatible with those values for Yemen (Abd Elmageed et al., this issue) and higher than the values reported in Jordan (Saqan et al., 2001), and lower than that reported in Nigeria (Agbalagba and Onoja, 2011) and Sudan (Alfatih et al., 2008). The 232Th activity concentrations are higher than the values reported in Yemen (Abd El-mageed et al., this issue) and Sudan (Alfatih et al., 2008) for lakes water and lower than that reported in Nigeria (Agbalagba and Onoja, 2011) and Sudan (Alfatih et al., 2008) for ground water. The 40K values in the present study are higher than the values reported in Table 9. The values of the absorbed dose rate, Hex and Hin are lower than unity and lower than the values reported in Nigeria (Agbalagba and Onoja, 2011).

4. Conclusion This study is a new detailed radioactivity concentrations and radiation hazard indices in NMP. The levels of natural radioactivity in the studied sites were found to be not exceeding the norm (Hex and Hin o1), except for soil sampling sites n025 and n 026. The low concentrations for 226Ra, 232Th, and 40K measured in some soil samples means that these soil and water in this study are suitable for use for agriculture and as building materials. Also, these water are suitable and safe for use in household and industrial purposes. 226Ra, 232Th, and 40K concentrations in water samples were found to be less than the permissible limits and with no contamination found in the study area as compared with other countries. The average value Raeq is 186 (in the range of 63–414) Bq kg 1 and 20 (in the range of 9.9–27.7) Bq kg 1 for soil and water, respectively, which are less than the 370 Bq kg 1 and 49 Bq kg 1 recommended maximum levels of radium equivalents in soil and water, respectively. A good correlation was observed between 226Ra and 222Rn concentrations, R¼0.81. This work has established baseline information on the natural radioactivity status of NMP, which will serve as a reference for future studies.

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