Radioactive contents and background doses from northern alluvial sediment plains between rivers Ravi and Chenab, Pakistan

NUCLEAR CHEMISTRY, RADIOCHEMISTRY, RADIOPHARMACEUTICALS AND NUCLEAR MEDICINE

Radioactive contents and background doses from northern alluvial sediment plains between rivers Ravi and Chenab, Pakistan

JABBAR Abdul，

KHAN Khalid，

TANIA Jabbar，

RAFIQUE Muhammad ，

S U Rehman，

WAHEED Arshed，

DILBAND Muhammad

Nuclear Science and Techniques

Vol.27, No.4

Article number 94

Published in print 20 Aug 2016

Available online 13 Jul 2016

DOI：10.1007/s41365-016-0085-7

43500

Radiometric analysis of soil samples, collected from northern alluvial sediment plains between rivers Ravi and Chenab, have been carried out. Activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K and the artificial radionuclide ¹³⁷Cs were estimated by using high purity germanium detector (HPGe). Subsequent values of activity concentrations were used to find terrestrial absorbed dose rate and annual effective doses received by resident of area. The mean radioactivity levels of ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs were found to be 45.0±1.3, 59.6±2.8, 613.8±20.0 and 4.0±0.2 Bq kg^-1 respectively. Terrestrial absorbed dose rate and annual effective dose received by public was found 85.1 nGy h^-1 and 0.5 mSv respectively. The activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs and resulting doses obtained for the current study were compared with data available in literature and with international standards.

Alluvial sediment plainsGamma-ray spectrometryradioactivityanthropogenic/primordial radionuclidesradiation doses

1 Introduction

Soil has got central position in all the environmental issues. Man has an intimate relation with the soil where he lives. All his food is grown in soil. Thus any change in the top layers of soil is bound to affect the man in one or the other way. Radionuclide’s presents in soil are important components of soil pollution. Primordial radionuclide’s ²³⁸U, ²³²Th, ⁸⁷Rb and ⁴⁰K contributes predominant part of the radioactivity in upper layers of the soil, whilst, anthropogenic radionuclides, ¹³⁷Cs and ⁹⁰Sr are also present in the soil originating from nuclear weapon tests, medical procedures and from nuclear accidents. These primordial and anthropogenic radionuclide’s are source of human exposure to back ground radiations [1].

Natural background radiation coming from terrestrial sources, not only, varies worldwide but also within the country. Knowledge about the distribution pattern of both anthropogenic and natural radionuclides is essential in maintaining some sense of control in prevailing radiation levels. In addition, it also provides information about the naturally occurring sources in the soil. Among main contributions from natural exposures from soil are ²³⁸U, ²³²Th series,⁴⁰K [2] and ¹³⁷Cs which is an important fission product from fall out [3]. ²³⁸U, ²³²Th and ⁴⁰K are also known as primordial radionuclides. These radionuclides compose a significant portion of the natural radionuclides present on earth because they are significantly long-lived and havehalf-lives long enough to have been present at the beginning of the earth’s formation [4, 5].

The study of the background level of ¹³⁷Cs in soil is very important since it is the main source of inventory of radionuclides entering into the food cycle. Its presence in soil would clearly indicate that the area under study might have received some fallout radioactivity in the past [6-8].

Due to increased public awareness about radioactive pollutants, it was decided to analyze the soil for radioactive contentsof northern alluvial sediment plains between rivers Ravi and Chenab, Pakistan. This paper deals with the measurement of decay products of uranium/thorium series, primordial radionuclide ⁴⁰K and ¹³⁷Cs in soil samples taken from various parts of the study area. The study of these radionuclides is very important due totheir radiological hazards. Some of these radionuclides have tremendous biochemical and geological tracers in the environment. In this perspective, activities of radionuclides ²²⁶Ra, ²³²Th series, ⁴⁰K and ¹³⁷Cs are being determined worldwide and the data is available in literature for many countries. The soil radioactivity levels of the above mentioned gamma emitting radionuclides have been assessed through gamma spectrometric technique innorthern alluvial sediment plains of Rechna Doab, Pakistan comprising of districts Sialkot, Narowal, Gujranwala and Hafizabad and discussed in this paper.

2 Study Area

The interfluvial region between rivers Ravi and Chenab, can be classified as one of the main regions of Punjab. Plain areas of Punjab are divided into natural regions based on its various rivers and the name Punjab is also based on its 5 main rivers. It comprising about 28,500 square kilometer is enclosed by the river Chenab and river Ravi on the Northwest and Southeast respectively, with the piedmonts near the Jammu and Kashmir boundary in the Northeast. It lies between longitude 71^o 48' to 75^o 20' E and latitude 30^o 31' to 32^o 51' N. It is about 403 kilometer, in southwest direction and has a maximum width of about 113 km [9].

The area is southwesterly sloped. In the upper part of the study area, the slope is about 38 cm/km to about 29 cm/km [10]. The alluvial fill is more or less homogeneous in nature, and has little continuityvertically or laterally, indicating diverse depositional environments from time to timecaused by constant change in the stream courses [11,12].The alluvial sediments mainly consist of gray, a grayish brown, fine to medium sand, siltand clay. Gravel or very coarse sand is uncommon.

3 Experimental Section

Systematic soil samples were collected from four districts of the study area by using a stainless steel coring tool according to spacial grids of 24 km × 28 km. A Global Positioning System (GPS) was also used in order to record coordinates of sampling locations for the purpose of traceability of the sampling place [13, 14].The sampling area is shown in Fig. 1.

Fig-1.

Map of study area, northern alluvial sediment plains between Rivers Ravi and Chenab, Pakistan

The chosen sampling sites were in open and plain land, covered with short-cropped grass, having moderate to good permeability and believed to be undisturbed for the last ten years, since these places were on un-cultivated land [15]. An area of 3 m×3 m was marked at every sampling location and the top 0.5 cm surface along with vegetation was removed prior to taking the sample. About 2 kg of soil sample comprising 5 cores was collected from selected area using coring device and was thoroughly mixed to prepare one representative sample. Pebbles, plant remains and other non relevant things were removed as per standard sampling methodology [16].These samples were packed into neat polyethylene bags and marked for later identification.

The samples were dried on polyethylene sheets at room temperature for one weekunder a controlled environment to avoid local dust contamination [17]. The samples were heated in an electric oven at 110^oC up to 48 h in order to remove moisture contents. This time was found enough to attain constant sample weight. After drying process, the samples were crushed; ground/pulverized in order to attain a predetermined particle size as dictated by the analytical requirements.The treated samples were then passed through a sieve having 2 mm mesh size. Homogenized samples having weight of 200 g were taken and packed in plastic containers with same geometry as that of reference materials, as dictated by the calibration requirement [18, 19]. These containers were sealed hermetically in order to stop gas leakage as a result of overpressure produced inside by emanation of ²²²Rn from ²²⁶Ra decay. After ensuring establishment of secular equilibrium among the progenies of ²³⁸U and ²³²Th decay series, these sealed samples were ready for gamma counting. A period of thirty days was enough to ful fill this requirement.

Radiometric analysis of these samples was performed using PC based high resolution gamma spectrometry system [20]. It comprised of high purity germanium (HPGe) coaxial detector having relative efficiency 30% with respect to NaI(Tl) detector, active volume of 180 c³fitted with beryllium-end window. The energy resolution was 2.0 keV FWHM at 1332 keV from ⁶⁰Co. The detector was shielded by 15 cm thick lead having inner lining of 3mm thick copper and 4 mm thick tin in order to reduce the background. The inner size of shielded cavity was 25 cm ×25 cm [21, 22]. The system was calibrated using IAEA soil-326 and reliability of counting efficiency was confirmed using IAEA soil-375 reference material. Samples were counted for 6.5×10³ seconds and the accumulated spectral data was analyzed by commercially available software GENIE-2000, obtained from Canberra, USA. Concentrations of ²²⁶Ra,²³²Th, ⁴⁰K and the fission product ¹³⁷Cs were determined by using the gamma lines of 351.99 keV, 911.07 keV, 1460.75 keV and 661.62 keV respectively.

The terrestrial gamma radiation dose rate survey was performed by using the radiation dose rate meter from FAG Germany model FH40F4. It employed a G.M. tube as active detector having energy independent response from 45 keV to 1.3 MeV. The reliability of the dose rate meter results was assured by its calibration in the Secondary Standard Dosimetry Laboratory (SSDL), PINSTECH, Pakistan, whose measurements are traceable to Primary Standard and are ensured by the International Atomic Energy Agency (IAEA) through postal dose inter-comparison [23].

The measurements were made 100 cm above the ground in open air. Ten readings were taken at each spot from where the soil sample taken and the average is recorded and their mean value was converted to absorbed dose rate in air (nGy h^-1).

4 Results and Discussion

Radioactivity levels of ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs measured in the soil of different areas collected in the present study are presented in Table 1.

Activity concentrations (Bq kg^-1) of ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs in soil samples of northern alluvial sediment plains between Rivers Ravi and Chenab, Pakistan.

Sr. No.	Sampling location	Latitude	Longitude	Activity concentration (Bq kg^-1)
				²²⁶Ra	²³²Th	⁴⁰K	¹³⁷Cs
1.	Gujranwala	32^o 09^/ N	74^o 07^/ E	32.8±1.5	41.8±2.7	480.2±19.5	2.1±0.1
2.	Wazirabad	32^o 28^/ N	74^o 05^/ E	39.3±1.5	57.5±2.8	652.8±20.2	≤MDA
3.	Aiman Abad	32^o 01^/ N	74^o 13^/ E	31.7±1.1	49.8±2.7	465.9±19.5	1.6±0.1
4.	Dhaunkal	32^o 23^/ N	74^o 08^/ E	51.5±1.2	61.5±2.8	695.9±20.3	3.2±0.2
5.	Ahmad Nagar	32^o 20^/ N	73^o 59^/ E	38.6±1.2	53.5±2.8	566.5±19.9	1.8±0.1
6.	Head Khanki	32^o 22^/ N	73^o 59^/ E	62.8±1.3	74.8±2.9	624.0±20.1	≤MDA
7.	Rasul Nagar	32^o 19^/ N	73^o 47^/ E	60.1±1.3	72.7±2.9	609.6±20.0	≤MDA
8.	Kalianwala	32^o 17^/ N	73^o 44^/ E	55.3±1.3	60.3±2.8	595.3±19.9	1.6±0.1
9.	Kot Hara	32^o 16^/ N	73^o 41^/ E	47.5±1.2	63.1±2.8	537.7±19.8	≤MDA
10.	Rasulpur Tarar	32^o 03^/ N	73^o 27^/ E	44.5±1.6	59.5±2.8	638.4±20.1	1.8±0.1
11.	Gajar Gola	32^o 04^/ N	73^o 43^/ E	54.3±1.6	59.1±2.8	739.0±20.5	≤MDA
12.	Uddowali	32^o 06^/ N	73^o 54^/ E	48.2±1.2	59.5±2.8	624.0±20.1	2.9±0.2
13.	Qillah Didar Singh	32^o 07^/ N	73^o 59^/ E	43.8±1.2	59.1±2.8	638.4±20.1	≤MDA
14.	Nosherah Virkan	31^o 59^/ N	74^o 09^/ E	50.9±1.6	58.7±2.8	695.9±20.3	2.9±0.2
15.	Kamoke	31^o 56^/ N	74^o 13^/ E	40.0±1.5	53.1±2.7	566.5±19.9	2.4±0.1
16.	Sadhuke	31^o 53^/ N	74^o 14^/ E	56.6±1.3	67.5±2.9	695.9±20.3	≤MDA
17.	Manguke	31^o 47^/ N	74^o 01^/ E	53.9±1.2	62.3±2.8	739.0±20.5	4.7±0.2
18.	Hafizabad	32^o 03^/ N	73^o 42^/ E	52.1±1.2	57.5±2.8	681.5±20.3	≤MDA
19.	Pindi Bhattian	31^o 53^/ N	73^o 15^/ E	51.5±1.2	67.9±2.9	595.3±19.9	≤MDA
20.	Winekay Tarar	32^o 13^/ N	73^o 35^/ E	46.5±1.7	61.5±2.8	667.2±20.2	1.6±0.1
21.	Chak Bhatti	32^o 05^/ N	73^o 24^/ E	47.9±1.5	69.1±2.9	595.3±19.9	≤MDA
22.	Jalal Pur Nau	32^o 03^/ N	73^o 23^/ E	44.9±1.2	59.9±2.8	624.0±20.1	≤MDA
23.	Sukhay Ki	31^o 49^/ N	73^o 35^/ E	44.5±1.2	52.3±2.7	595.3±19.9	3.3±0.2
24.	Kishan Garh	31^o 47^/ N	73^o 26^/ E	58.5±1.8	73.6±2.9	739.0±20.5	5.5±0.2
25.	Sialkot	32^o 27^/ N	74^o 33^/ E	36.2±1.1	51.0±2.7	580.9±19.9	6.3±0.2
26.	Sambrial	32^o 30^/ N	74^o 20^/ E	33.2±1.1	47.4±2.7	451.5±19.4	2.2±0.1
27.	Kulu Wal	32^o 34^/ N	74^o 21^/ E	49.5±1.2	66.3±2.8	652.8±20.2	5.6±0.2
28.	Head Marala	32^o 40^/ N	74^o 28^/ E	42.2±1.2	55.9±2.8	624.0±20.1	3.6±0.2
29.	Chaprar	32^o 34^/ N	74^o 29^/ E	41.2±1.2	55.9±2.8	537.7±19.8	4.6±0.2
30.	Chuvinda	32^o 21^/ N	74^o 37^/ E	36.9±1.1	60.7±2.8	609.6±20.0	8.1±0.3
31.	Mundeki	32^o 17^/ N	74^o 32^/ E	43.0±1.2	69.9±2.9	695.9±20.3	3.8±0.2
32.	Daska	32^o 17^/ N	74^o 21^/ E	46.0±1.2	60.3±2.8	638.4±20.1	4.2±0.2
33.	Dharamkot	32^o 11^/ N	74^o 22^/ E	46.8±1.2	64.7±2.8	667.2±20.2	6.9±0.2
34.	Sutra	32^o 09^/ N	74^o 28^/ E	40.8±1.2	56.3±2.8	480.2±19.5	≤MDA
35.	Merajke	32^o 24^/ N	74^o46^/ E	38.0±1.2	51.8±2.7	580.9±19.9	5.6±0.2
36.	Norowal	32^o 06^/ N	74^o 51^/ E	37.5±1.1	59.1±2.8	667.2±20.2	2.0±0.1
37.	Zafarwal	32^o 20^/ N	74^o 55^/ E	36.0±1.1	48.2±2.7	566.5±19.9	7.3±0.2
38.	Chak Amro	32^o15^/ N	74^o 08^/ E	41.8±1.2	62.7±2.8	537.7±19.8	6.1±0.2
39.	Noor Kot	32^o 11^/ N	74^o 06^/ E	39.9±1.2	59.9±2.8	537.7±19.8	3.0±0.2
40.	Jassar	32^o 05^/ N	74^o 55^/ E	39.3±1.2	59.5±2.8	710.3±20.4	7.2±0.2
41.	Talwindi Bhindran	32^o 06^/ N	74^o 40^/ E	39.2±1.2	60.3±2.8	566.5±19.9	≤MDA

It can be seen in this table that the activity of ²²⁶Ra ranges from 31.7±1.1Bq kg^-1 in Aiman Abad to 62.7±1.4 Bq kg^-1 in Head Khanki. The activity of ²³²Th ranges from 41.8±2.7Bq kg^-1 in Gujranwala to 74.8±2.9Bq kg^-1 in Head Khanki. The activity of ⁴⁰K ranges from 451.5±19.4Bq kg^-1 in Sambrial to 739.0±20.5Bq kg^-1 in Kishan Garh. The radioactivity level of artificial radionuclide ¹³⁷Cs is found to be the maximum in Chuvinda (8.1±0.3Bq kg^-1). The radioactivity levels of ⁴⁰K are seen to be higher than those of ²³²Th and ²²⁶Ra at all the places of study area. In order to determine the existing ratio between the activity concentrations of three natural radionuclides in soil samples, correlations between them were drawn.

Figs. 2(a-c) represents correlations between the activity concentration of ²²⁶Ra and ²³²Th, ²²⁶Ra and ⁴⁰K and ²³²Th and ⁴⁰K respectively, with a trend line drawn among the data points using regression technique. In all the three cases, the regression was found linear and positive. A trend line is the most reliable when its R-squared value is at or close to 1. The correlation coefficient between ²²⁶Ra and ²³²Th is 0.6 where as between ²²⁶Ra and ⁴⁰K and similarly between ²³²Th and ⁴⁰K it is quite low. It indicates that ²²⁶Ra and ²³²Th come from a common origin where as ⁴⁰K has source that is independent of both ²²⁶Ra and ²³²Th. However a positive correlation may still be attributed to property of the soil in retaining these radionuclides under varying weather conditions. The results shown in Table 1 also indicate that the mean value of ⁴⁰K is the highest and that of ²³²Th is the lowest.

Fig. 2.

(a) Correlation between ²²⁶Ra and ²³²Th concentrations; (b) correlation between ²²⁶Ra and ⁴⁰K concentrations; (c) correlation between ²³²Th and ⁴⁰K concentrations.

¹³⁷Cs, although at very low concentrations, was detected at most of the places. Its concentration ranged from 1.6±0.1 to 8.1±0.3Bq kg^-1 with an average value of 4.0±0.2 Bq kg^-1. At some locations its concentration was quite low and less than minimum detectable activity (MDA; 1.4 Bq kg^-1). ¹³⁷Cs is one of the important fission products and is a prominent indicator of fall out from nuclear weapon tests during fifties and sixties of last century and the fallout due to the Chernobyl accident [8].

The statistics of the values measured for ²²⁶Ra, ²³²Th and ⁴⁰K in the surface soil samples are enlisted in Table 2. Itshows the respective mean value, range, median, skewness, kurtosis coefficients and the type of theoretical frequency distribution that best fits each empirical distribution. It is observed that the values of skewness and kurtosis coefficients for ²²⁶Ra, ²³²Th and ⁴⁰K activities and also in absorbed dose rates are closer to the null value, indicating the existence of normal distribution and the activityconcentration is practicallysymmetrical, as shown in Figs. 3(a–d).

Statistical data for radioactivity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K and dose rate in surface soil samples from northern alluvial sediment plains, Pakistan

	Activity concentration (Bq kg^-1)			Dose rate (nGy h^-1)
	²²⁶Ra	²³²Th	⁴⁰K	Dose rate (nGy h^-1)
Mean	45.00	59.64	613.84	85.09
Std. Dev.	7.737	7.149	74.38	9.83
Median	44.47	59.48	624.01	85.65
Skewness	0.406	-0.014	-0.297	-0.239
Kurtosis	-0.498	0.273	-0.368	-0.009
Range	31.74 – 62.77	41.80 – 74.75	451.47 – 739.04	62.30 – 105.44
Frequency Distribution	Normal	Normal	Normal	Normal

Fig-3.

Frequency distribution of the activities of (a) ²²⁶Ra, (b) ²³²Th, (c) ⁴⁰K (Bq kg^-1 dry weight) and d) calculated terrestrial absorbed dose rate at 100 cm above ground (nGy h^-1).

The existence of a wide range in the variation of the activities of radionuclide’s is also observed (Table 2). This is due to thewide variety of lithological components existing in the zone under study.

We have also calculated gamma dose rate (D) in the outdoor air at 100cm above the ground level using the conversion factor published in UNSCEAR 1988 [24]. To do so, the following equation[25]was used

D = (6.62 C_{Th} + 4.27 C_{Ra} + 0.43 C_{K}) \times 10^{- 10} G y h^{- 10}

(1)

where C_Th, C_Ra and C_K are the average activity concentrations of thorium, radium and potassium, respectively. The absorbed dose rate ranges from 62.3 nGy h^-1 in Gujranwala to 105.4nGy h^-1 in Kishan Garh. One of the objectives of measuring radioactivities was to make an estimate of radiation dose likely to be delivered to the general public externally.

The in-situ gamma dose rate at 100cm above the ground has also been measured using an environmental radiation dose rate meter (FAG). The average measured gamma dose rate is 109.05 nGy h^-1. The average dose rate calculated from soil measurements for the same area is 85.09 nGy h^-1, which is less than the in-situ measurements as shown in Fig. 4. It was observed that measured absorbed dose rate values are 1.2 to 1.3 times higher than the calculated values.This difference is expected as FAG dose rate meter is also responsive to cosmic rays, high energy beta particles and X-rays.

Fig-4.

Comparison of measured and calculated dose rates in study area, northern alluvial sediment plains between Rivers Ravi and Chenab, Pakistan

As shown in Table 3, the mean activity of ²²⁶Ra measured in the soil of study area (45.0±1.3 Bq kg^-1) is higher than that of many countries like Venezuela [26] and Taiwan [27] etc. However, it is lower than that of Turkey [28] and Indian Punjab and Himachal Pradesh [29].The World average [30] is also higher than the values determined in present study. Some Pakistani areas like Lahore [31], Punjab Province [32], Southern Punjab [33] and Mirpur Azad Kashmir [34] have lower²²⁶Ra level than northern alluvial sediment plains, Pakistan.

Activity concentrations (Bq kg^-1) of ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs in soil samples reported from different countries of the world.

Area	Mean activity concentration (Bq kg^-1)				Dose rate (nGy h^-1)	Reference
	²²⁶Ra	²³²Th	⁴⁰K	¹³⁷Cs
Turkey	79	62	574	-	100	[27]
Indian Punjab and Himachal Pradesh	56.74	87.42	143.04	-	86.54	[28]
Taiwan	30	44	431	-	54	[26]
Venezuela	27	31	357	5	-	[25]
World Average	50	50	500	-	70	[29]
Southern Punjab, Pakistan	21.7	31.1	393.2	1.6	46.1	[32]
Punjab Province, Pakistan	35	41	615	-	68	[31]
Lahore, Pakistan	25.8	49.2	561.6	-	65	[30]
Northern alluvial sediment plains, Pakistan	45.0	59.6	613.8	4.0	85.1	Present study

Similarly, the level of ²³²Th in northern alluvial sediment plains is 59.6±2.8Bq kg^-1. Its values are more than those in Taiwan, Venezuela and world average but lower than that of IndianPunjab and Himachal Pradesh and Turkey.

To check and calculate how much effective dose equivalent will be received by the public due to activity in soil, the annual effective dose was calculated using the formula [35];

E_{air} = T Q D_{air} \times 10^{- 6} ，

(2)

where D is the absorbed dose rate in air, Q the conversion factor of 0.7 Sv Gy^-1, which converts the absorbed dose in air to human effective dose in adults and T the time in hours for 1 y, i.e. 8760 h [36].The calculated values of annual effective dose (E) for all samples are shown in Table-2 Annual effective dose lies in the range 0.22-0.37 mSv with a mean of 0.30 mSv.

5 Conclusion

This is the first systematic study to establish a baseline data of primordial and anthropogenic radionuclide’s in the Rechna Doab, Pakistan. In future to make the studymore comprehensive, the grid size to collect soil samples can be reduced to obtain the background radiation levels which are relatively more representative of the area. A study can be made to know the levels of NORMS in soils which are being used largely through phosphate fertilizers and industries dumping their effluents in thesoil. On the basis of our results we conclude that the soil of the study area do not pose any radiological health hazard to the public of the area.

References

Collado G M.

Radionuclide Concentrations in Soils

. In: M Pöschl, L M. L. Nollet (Eds.), Radionuclide Concentrations in Food and the Environment, Taylor & Francis, Boca Raton, 2006,ISBN 9780849335945.