Journal of Radioanalytical and Nuclear Chemistry (2019) 320:291–298
https://doi.org/10.1007/s10967-019-06481-1
Activity concentrations of radionuclides in soil samples
along the coastal areas of Kerala, India and the assessment
of radiation hazard indices
M. Ramsiya1 · Antony Joseph1 · K. P. Eappen2,3 · A. K. Visnuprasad4
Received: 11 October 2018 / Published online: 19 March 2019
© Akadémiai Kiadó, Budapest, Hungary 2019
Abstract
The present study was carried out along the coastal regions of Kerala, India, to evaluate the distribution of uranium, thorium
and potassium concentrations in surface soil samples. A total of 92 soil samples were collected from 9 coastal districts, lying
by the side of the Arabian Sea. The radium equivalent activities in the beach sands of Kollam district varies from 877 to
3715 Bq kg−1, which is higher than the reference limit of 370 Bq kg−1. Results show that the radiological parameters obtained
for the beach sand from the districts of Thiruvananthapuram, Alapuzha, Eranakulam, Thrissur, Malappuram, Kozhikode,
Kannur and Kasaragod are within the safe limits and hence these places can be considered as Normal Background Radia-
tion Areas. Thus, when the high radioactive places are confined to a narrow belt in Kollam district, the other coastal areas
of Kerala, especially northern and middle zones are within the safe limit with respect to radiological index.
Keywords Thorium · Monazite · Kerala coasts · Radiological parameters · Activity concentrations · Radium equivalent
activity
Introduction Further, the possible impact of natural radiation on the
biota (including man) has been a matter of serious concern
In India, the occurrence of monazite sand bearing placer from societal and biological stand-points. Many studies have
deposits, causing emission of natural radiation along its been reported over the years, with results on varying natural
long coastal line, had been reported earlier [1]. Odissa [2, radioactivity even for same locations [6, 10, 11].
3], Ullal in Karnataka [4], Kalppakkam in Tamil Nadu [5], India has a long coastal line of 7516 km. Kerala, the south
Neenkaraka—Chavara of Kerala coasts [6, 7] and the south part of India is having monazite deposits in southern part of
western coast of India are known to be High Background its coastal regions. Monazite sand present in Kerala region
Radiation Areas (HBRAs) [8]. Studies in these places had is found to have ~ 0.35% uranium and ~ 9% thorium oxides
created considerable interest, primarily due to the geological together with other minor rare earth compounds. In addi-
reasons in as much as monazite, the rich source of radioac- tion to this, the beach sand along Chavara—Neendakara in
tive uranium and thorium, an important component in the Kollam district is rich in ilmenite, rutile, zircon and garnet,
sand from HBRAs [9]. Besides monazite, the beach placer offering potential scope for exploration in industrial uses
deposits may contain zircon, ilmenite, rutile, and garnet. [12]. Natural radiation is largely caused by the presence of
primordial radionuclides and their decay products present in
nature. Since the coastal areas of Kerala is generally consid-
* M. Ramsiya
[email protected] ered as coming under the HBRA, a detailed study detailed
study covering the entire coastal belt of Kerala is essential
1
Department of Physics, University of Calicut, to exactly pinpoint the places which belonging to NBRA
Kerala 673635, India and HBRA. Usually data from marine coastal monitoring of
2
BARC, Mumbai, India radioactivity acts as a baseline for the assessment of radioac-
3
IEC, New Delhi, India tive pollution experienced by the biota.
4
Department of Physics, Fatima Mata National College, The terrestrial radioactivity in soil is estimated by evalu-
Kollam, Kerala, India ating the activity concentrations of primordial radionuclides
13
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292 Journal of Radioanalytical and Nuclear Chemistry (2019) 320:291–298
such as 238U, 232Th and 40K. The radionuclides 238U, 232Th The spectrum of gamma rays emitted by the samples was
and 40K are aberrantly distributed in earth’s crust and the generated using a HPGe detector having a relative efficiency of
geographical variation of the radionuclides are due to soil 21%, with an energy resolution of 1.7 keV for 1.33 MeV peak
erosion, weathering of rocks, selective leaching of elements of 60Co. The detector was coupled with DSPEC digital signal
etc. Thus as mentioned earlier, the main objective of the processing unit that includes a high voltage filter, preampli-
present work is to carry out an extensive study of the pri- fier and 32 K display memory. The detector was shielded by
mordial radionuclides like uranium, thorium and potassium cylindrical lead blocks with fixed bottom and removable lid to
present in the entire coastal areas of Kerala and to evaluate reduce the background. The energy calibration was done using
60
their radiological parameters. Co, 137Cs, 22Na, and 133Ba sources. The efficiency calibra-
tion of the system was carried out using the IAEA reference
Region of the study standard ore samples RGU-1 and RGTh-1, taken in contain-
ers having same dimension as that of the samples. The activ-
Surface soil samples weighing 1.5–2 kg were collected from ity of uranium was estimated by measuring the area under
17 locations along the coastal areas of Kerala, extended over the photo peaks of 214Pb (351.9 keV) and 214Bi (609.3 keV).
a length of 590 km, with Arabian Sea on the west. Kerala Thorium activity was determined from the photo peaks of
228
constitutes 10% of India’s coastal zone, with an exclusive Ac (911.2 keV), 212Pb (238.6 keV) and 208Tl (583.2 keV).
40
economic zone (EEZ) of 218,536 Sq km. Fisheries have K activity was measured directly from the full energy photo
prominent contribution to the Kerala economy and fisher- peaks corresponding to 1460 keV.
men population is around 10 lakhs, living in the 222 marine The activity (A) of primordial radionuclides in soil samples
villages [13]. The density of population in the coastal area were calculated by using the equation
of Kerala is 2168 persons per km2, whereas that of the state ( )
Bq C
average is 859. Among the 14 districts of Kerala, 9 districts A = (1)
kg
are sharing the coastal zone. Kerala’s coastal belt is almost
𝜀𝛾tm
flat and mostly utilized as paddy fields, interconnected by where C is counts above background, ε is the absolute effi-
canals and rivers. The natural hazards like landslides, coastal ciency of the detector, γ is the absolute gamma ray transition
erosion, flooding and tsunami happen in coastal zones. The probabality, t is the aquisition time and m is the mass of the
sampling areas selected for the present study are from the sample in kg.
coastal regions of Thiruvananthapuram, Alappuzha, Kollam,
Ernakulam, Thrissur, Malappuram, Kozhikode, Kannur, and Radiation hazard indices
Kasaragod districts. Figure 1 gives the sampling areas cov-
ered for the study. The absorbed dose rate (D) due to gamma radiation in air at
1 m above the ground surface, is calculated using Eq. (2),
based on the guidelines provided by UNSCEAR, 2000. Uni-
Materials and methods form distribution of the naturally occurring radionuclides
(238U, 232Th and 40K) is assumed for the calculation.
An average of 5–10 soil samples were collected from each ( )
sampling location. Samples were collected at 10 m interval at nGy
D = 0.461AU + 0.623ATh + 0.043AK (2)
the sampling area, depending on the contour and lay out. Indi- h
vidual sample is collected from 1 m2 area. The sampling area
where AU, ATh and AK are activity concentrations of 238U,
is then divided into 16 equal squares. After removing the upper 232
Th and 40K in Bq kg−1 at the sampling location.
layer of the soil, sample is collected up to 5 cm depth from the
To assess the health effects caused by the radionuclides,
middle of each square and combined to make a gross sample
the annual effective dose (AED) received by the population
of approximately 1.5–2 kg from each sampling location. The
for outdoor exposure is determined using the dose conversion
samples thus collected were then dried in an oven at 110 °C
coefficient 0.70 Sv year−1 for the total exposure (Gy) during
for 24 h to remove the moisture content. Each sample was then
the year. For outdoor exposure, the occupancy of 0.2, as sug-
homogenised and sieved through 0.5 mm size mesh. The sam-
gested by UNSCEAR 2000 [14] is taken. Accordingly the
ples were then hermetically sealed, weighed and stored in air
AED is calculated using Eq. (3)
tight plastic containers of diameter 6.5 cm and height 8.4 cm
for a period of 4–6 weeks to attain secular equilibrium between
( ) ( ) ( )
mSv nGy Sv
AED =D × 8760 × 0.2 × 0.7 × 10−6
parent and daughters of the uranium and thorium series. The y h Gy
samples were then counted for gamma activity for a period of (3)
36,000 s to get a reasonable area under the photo-peaks, cor-
responding to various gamma energies.
13
Journal of Radioanalytical and Nuclear Chemistry (2019) 320:291–298 293
Fig. 1 Sampling locations
where D (nG h−1) is the absorbed dose rate in the outdoor Eq. (5) where 232Th, and 40K activities are normalised to
air and 8760 h is the number of hours in 1 year. that of 238U values, considering the radiological effect
Radium equivalent activity ( Raeq), a widely used hazard from the elements.
index, was calculated using Eq. (4) [15, 16].
AU A A
( )
Bq Hex = + Th + K . (5)
370 259 4810
Raeq = AU + 1.43ATh + 0.077AK . (4)
kg
The radiological suitability of a material is usually
expressed in terms of the external hazard index Hex. If Hex Results and discussion
index is greater than unity, then the exposure received by
the individual exceeds the recommended limits and reme- A total of 92 samples were collected from 17 sampling
dial action is required [17]. Hex index is evaluated using locations for the study. The average activity concentration
(238U, 232Th and 40K) for each sampling area is presented in
13
294
13
Table 1 The uranium, thorium and potassium activity in 17 locations, distributed over 9 coastal districts
238 232 40
Sl. no. Sampling area No of samples Geographic U (Bq kg−1) Th (Bq kg−1) K (Bq kg−1)
coordinatesa
N E AM ± SD Min. Max. AM ± SD Min. Max. AM ± SD Min. Max.
1 Thiruvananthapuram 3 8°40′ 76°98′ 20.00 ± 1.52 18.25 21.02 34.64 ± 4.34 30.76 39.32 161.53 ± 11.70 150.54 173.83
2 Neendakara Jyothi 8 8°88′ 76°59′ 507 ± 188 250 767 1311 ± 598 568 2232 151.93 ± 32.65 78.54 189.63
3 Neendakara 10 8°94′ 76°54′ 513 ± 228 65 927 1365 ± 687 103 2614 166.94 ± 17.19 145.36 205.38
4 Parimanam 5 8°95′ 76°53′ 545 ± 24 508 570 1570 ± 598 103 2614 148.39 ± 10.57 134.41 163.58
5 Karithura 6 8°97′ 76°52′ 1089 ± 80 967 1176 1818 ± 837 1142 3485 363.56 ± 52.06 296.33 436.52
6 Chavara IRE 5 8°98′ 76°52′ 204 ± 108 85 345 933 ± 343 186 991 175.88 ± 13.99 164.96 203.23
7 Chavara 10 8°99′ 76°54′ 326 ± 174 170 747 888 ± 594 273 2291 180.96 ± 22.21 131.00 221.62
8 Alapuzha 3 9°35′ 76°36′ 37.30 ± 10.25 28.80 48.60 49.71 ± 19.41 34.76 71.65 156.14 ± 20.92 138.68 179.32
9 Eranakulam Cherai 5 10°14′ 76°17′ 5.92 ± 0.44 5.24 6.28 8.85 ± 0.87 7.54 9.77 233.84 ± 71.35 108.46 285.85
10 Kuzhuppilly 5 10°16′ 76°17′ 14.39 ± 1.36 13.28 17.04 51.42 ± 7.00 41.33 59.59 229.63 ± 21.02 190.46 251.34
11 Munampam 4 10°18′ 76°17′ 10.80 ± 0.60 10.11 11.54 26.39 ± 6.63 15.13 32.13 237.62 ± 20.68 216.16 262.14
12 Thrissur Vadanapilly 5 10°43′ 76°07′ 4.53 ± 0.77 3.31 5.21 7.93 ± 1.47 5.54 9.11 289.82 ± 14.07 279.14 313.41
13 Chavakkad 5 10°56′ 76°09′ 4.06 ± 0.53 3.17 4.46 6.53 ± 0.83 5.22 7.31 324.93 ± 46.36 286.14 385.04
14 Ponnani 4 10°77′ 75°93′ 18.07 ± 1.41 16.71 19.61 54.84 ± 9.63 43.68 67.07 258.45 ± 30.13 214.14 281.29
15 Kappad 4 11°38′ 75°73′ 5.27 ± 0.80 4.21 6.14 9.80 ± 1.08 8.52 11.01 220.43 ± 23.66 191.03 248.41
16 Payyambalam 5 11°86′ 75°35′ 4.28 ± 0.81 3.11 5.62 13.78 ± 3.59 10.11 19.07 160.90 ± 20.13 132.98 187.76
17 Bekal 5 12°42′ 75°23′ 2.04 ± 0.58 1.19 2.62 10.38 ± 1.78 7.83 12.43 141.13 ± 15.12 122.39 159.11
AM arithmetic mean, SD standard deviation
a
Latitude/longitude
Journal of Radioanalytical and Nuclear Chemistry (2019) 320:291–298
Journal of Radioanalytical and Nuclear Chemistry (2019) 320:291–298 295
the thorium and uranium activity in the samples collected
along the coastal area, average Th/U ratio of 1–4 is observed
(Fig. 2). These points towards the deposition of the monazite
sand along these areas from sea bed sand that might have
undergone preferential leaching of uranium in the samples.
Thorium has only one oxidation state Th (+ 4), and this is
insoluble in water [19]. But uranium has + 4 and + 6 valence
states and + 6 is more reactive and highly soluble compared
to + 4. In addition to leaching, the constant wave action and
the sedimentary process plays a key role in the distribution
of radioelements along the coastal areas.
In Kollam district, the samples were collected from
Neendakara, Neendakara-Jyothi, Parimanam, Chavara,
Chavara-IRE and Karithura. The activity of uranium and
thorium in all the analysed samples were higher than the
UNSCEAR 2008 reference limit (Fig. 3). The high radio-
activity along the coastal areas of Kollam district is due
to geographical reasons. Here Kallada River empties into
Fig. 2 The average value of Th/U ratio in each sampling location
Ashtamudi Lake and the Neendakara bar separates Ashta-
mudi Lake from Arabian Sea. The minerals were accumu-
lating in these areas (Neendakara-Chavara) by the fluvial
transport of minerals from granites, gneiss and charmokites,
existing in the hinterlands of Kerala [20]. The warkilli series
of rocks—the intermediate host rocks for monazites between
original source rocks and beach boulders, are also prevalent
in these areas.
The uranium, thorium and potassium levels in the
coastal areas of Thiruvananthapuram, Alapuzha, Eranaku-
lam, Thrissur, Kozhikode, Kannur and Kasaragod districts
show that at these locations the radioactivity levels are
less than the UNSCEAR 2008 reference limit [21]. How-
ever, the potassium activity is much higher than the radium
and thorium activity in the coastal areas of Thiruvanan-
thapuram, Alapuzha, Eranakulam, Thrissur, Malappuaram,
Kozhikode, Kannur and Kasaragod districts. These coastal
areas come under the normal background radiation areas
Fig. 3 Uranium, thorium and potassium activity concentrations in the
(NBRA), where the presence of monazite sand is neg-
coastal areas of Kollam district
ligible. Among the various beaches in the northern and
middle zones, thorium level (54.84 Bq kg −1) at Ponnani
Table 1. The origin of thorium deposits on the west coast in Malappuram district is comparable to the UNSCEAR
of India is not well established, though a number of studies 2008 reference limit (45 Bq kg −1). It is the place where
on the various aspects of these deposits have been carried Bharathapuzha River comes to end to join with the Ara-
out for more than 50 years [18]. An analysis of uranium to bian Sea. The coastal configuration along with the fluvial
thorium ratio in the rock samples and on the beach sand transportation of Bharathapuzha River from the hinterland
would be useful for speculating the age of deposition, keep- granulitic terrain parts of Kerala causes high thorium con-
ing in mind that generally thorium is less labile than ura- tent in Ponnani coastal region.
nium. The median values obtained worldwide for U, Th and Table 2 shows that except at Chavara-IRE, the annual
K are 7.4 µgg−1, 2.8 µgg−1, and 1.3%, respectively. These effective dose received by the population in the coastal areas
mean values were derived by transforming the correspond- of Kollam district is higher than the world wide average
ing worldwide average activity concentrations of 30, 35, value of 0.5 mSv year−1 [1]. The fishermen communities
and 400 Bq kg−1 [1]. The above values give an average which live in coastal areas spending their time for fishing
ratio close to 1 for Th/U activity. From the plot showing and related activities receive the radiation dose caused by
the radionuclides. The annual effective dose received by
13
296 Journal of Radioanalytical and Nuclear Chemistry (2019) 320:291–298
Table 2 Absorbed dose, annual Sl. no. Location Absorbed dose (D) Annual effective dose Hex index
effective dose and external (nGy h−1) (AED) (mSv year−1)
hazard index (Hex)
1 Thiruvanatapurm 37.75 ± 3.06 0.046 ± 0.004 0.22 ± 0.02
2 Neendakara Jyothi 1058 ± 457 1.298 ± 0.561 6.47 ± 2.81
3 Neendakara 1094 ± 533 1.343 ± 0.654 6.69 ± 3.27
4 Parimanam 1236 ± 362 1.517 ± 0.445 7.57 ± 2.25
5 Karithura 1651 ± 550 2.025 ± 0.676 9.98 ± 3.51
6 Chavara 712 ± 450 0.873 ± 0.553 4.35 ± 2.77
7 Chavara IRE 390 ± 222 0.478 ± 0.273 2.37 ± 1.36
8 Alapuzha 54.88 ± 17.72 0.067 ± 0.022 0.33 ± 0.11
9 Cherai 18.29 ± 3.18 0.022 ± 0.004 0.10 ± 0.02
10 Kuzhupilly 48.55 ± 4.59 0.060 ± 0.006 0.29 ± 0.03
11 Munampam 31.63 ± 3.82 0.039 ± 0.005 0.18 ± 0.02
12 Vadanapilly 19.49 ± 1.62 0.024 ± 0.002 0.10 ± 0.01
13 Thrissur 19.91 ± 2.48 0.024 ± 0.003 0.10 ± 0.01
14 Ponnani 53.61 ± 5.13 0.066 ± 0.006 0.31 ± 0.03
15 Kappad 18.01 ± 1.03 0.022 ± 0.001 0.10 ± 0.01
16 Payyambalam 17.48 ± 2.50 0.021 ± 0.003 0.09 ± 0.01
17 Bekal 13.47 ± 1.94 0.016 ± 0.002 0.07 ± 0.01
dose (D) (1651 ± 550 nGy h−1) was found at Karithura in
Kollam district and the lowest value was found at Bekal
(13.47 ± 1.94 nGy h−1) in Kasaragod district. The external
hazard index (Hex) in beaches of Kollam district varies from
2.37 to 9.98 which is greater than the value of 1 that is rec-
ommended for external exposure index. This indicates that
the hazardous effect caused by the surface beach sand is high
at these places. The Hex in the normal background areas of
Kerala (i.e., except Kollam district) varies from 0.07 to 0.33,
which is within the value recommended.
A plot of Raeq and absorbed dose, computed from the
data is presented at increasing order of location latitudes in
Fig. 4. Average values from the samples analysed at each
location with standard deviation (SD) is presented in this
graph. The peaks for both Raeq and Dose (D) are predomi-
nant in the area between 8.5 and 9.0 latitudes (coastal areas
of Kollam district), showing the beach deposit of monazite
in these areas.
Fig. 4 Raeq and absorbed dose received by the public in coastal areas
of Kerala The radioactivity levels in soil samples in different
coastal beaches of India and other countries are listed in
Table 3. The uranium activity in the HBRA (Kollam dis-
trict) is comparable to the well known HBRAs like Ullal in
the population in normal background areas (Thiruvanan- Karnataka whereas the thorium activity is less than that of
thapuram, Alapuzha, Eranakulam, Malappuram, Kozhikode, Odissa, and Ullal [3, 7]. The uranium levels in coastal areas
Kannur and Kasaragod districts) varies from 0.016 to 0.067 (NBRA) of Kerala are comparable to the nearby coastal
and hence it can be considered as negligible. parts of Tamilnadu [5, 22] but thorium is less than that at
In the present study, covering the entire coastal areas other studied NBRAs within India. Like the coastal areas
of Kerala, the absorbed dose rate in beach sand of Kol- of Kerala, the neighbouring state Tamilnadu also is hav-
lam district is found to be higher than the global mean ing high background [23] and normal background radiation
value of 60 nGy h−1 [1]. The highest value of absorbed areas [22]. The potassium activity in China [19, 26], Brazil
[27], Turkey [25] and Thailand [28] are higher than that at
13
Journal of Radioanalytical and Nuclear Chemistry (2019) 320:291–298 297
Table 3 Uranium, thorium Country 238
U (Bq kg−1) 232
Th (Bq kg−1) 40
K (Bq kg−1) References
and potassium levels in soils,
observed in various coastal Kollam-HBRA, Kerala, India 516 1229 194 Present study
areas within India and other
Coastal areas of Kerala-NBRA 10.10 23.16 241.94 Present study
countries
Southern region of Tamil Nadu coast 12.13 59.03 197.03 [22]
(HBRAs), India
North East coast of Tamilnadu, India 349 713 35 [23]
Odisha, Eastern India 274 2489 – [3]
Ullal, Karnataka, India 546 2971 268 [7]
Kalpakkam, Tamilnadu, India 16 119 406 [5]
Xiamen Island, China 14 11 401 [19]
Red sea coast-Safaga 25 21 61 [24]
Hurguda 20 22 548
Kirklareli, Turkey 37 40 667 [25]
Guangdong, China 134 187 680 [26]
Dois Rios beach, Brazil 6–78 12–87 269–587 [27]
East coast, Thailand 3–18 5–34 182–559 [28]
the coastal areas of Kerala. Table 3 shows that Indian coastal the tourists coming for the recreation and for the fisherman
areas [3, 5, 7, 22] are thorium enriched areas with less potas- community living around.
sium content, compared to other countries.
Acknowledgements One of the authors (Ramsiya M.) acknowledges
with thanks, UGC Govt. of India for MANF fellowship and for SAP
facilities in the department. The technical help received from Mr. Jam-
Conclusion shihas A P, Vishnu C V and Midhun C V are gratefully acknowledged.
The overall results show that radiation exposure due to natu- Funding The funding was provided by Ministry of Minority Affairs
ral radionuclides is high in the area of Neendakara—Chavara (Grant No. 22627).
region. Annual Effective Dose (AED) calculated from the
44 samples collected from Kollam district show a geomet-
ric mean value of 1.04 (GSD 2.03) mSv year−1. The study
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