Measurement of natural radioactivity level in surface sediment in southern Kuala Selangor coastal area

Kuala Selangor is located in Sungai Selangor estuary in the west coast of Peninsular Malaysia. Kuala Selangor coastal area is susceptible to pollution load as a lot of industrial and human activities are located in the west coast of Peninsular Malaysia and along Sungai Selangor. Surface sediment was taken from 14 points at two locations in southern Kuala Selangor that are in ‘Pantai Remis’ and ‘Pantai Jeram’. This study focused on radioactivity level of naturally occurring radionuclide (mainly Ra, Ra and K) in surface sediment using gamma-ray spectrometry with a high-purity germanium (HPGe) detector. For K, the presence of this was measured directly via its 1460 keV energy peak. For Ra (of the U) and Ra (of the Th) the γray lines 609.3 keV (Bi) and 911.1 keV (Ac) were used. The concentration of Ra, Ra and K in samples obtained from Pantai Remis coastal area ranged between 42.9±1.4-60.0±1.6 (mean 47.6±1.5) Bq/kg, 61.9±2.8-79.3±2.9 (mean 69.5±2.7) Bq/kg and 324.5±10.6-455.8±13.2 (mean 422.2±12.2) Bq/kg, respectively. Meanwhile, the concentration of Ra, Ra and K in samples obtained from Pantai Jeram coastal area ranged between 45.1±1.6-50.4±1.5 (mean 47.2±1.6) Bq/kg, 62.5±2.8-75.9±3.0 (mean 69.2±2.9) Bq/kg and 338.7±10.7-490.6±14.0 (mean 428.2±12.4) Bq/kg, respectively. The mean external hazard index due to these radionuclides is 0.484 for ‘Pantai Remis’ and ‘Pantai Jeram’ (less than unity). Thus, it is expected that no radiation hazard attributed to the radiation from the study radionuclides will be experience by people in the areas. | Natural radionuclide| Surface sediment| Activity concentration | Gamma spectrometer | Coastal area | ® 2012 Ibnu Sina Institute. All rights reserved. http://dx.doi.org/10.11113/mjfas.v8n4.163


INTRODUCTION
The two prominent sources of external radiation are cosmic rays and terrestrial gamma-rays which are derived mainly from naturally occurring radioactive materials (NORM) [1]. 226Ra, 228 Ra, and 40 K is NORM that present almost everywhere in the water, land and air.These radionuclides when deposited on the surface soil is washed and drained through rivers transport and finally ended in the estuary and entering the marine environment and also through several pathways such as weathering, erosion, fallout, rainwater and human activities [2].
Sediments which one of the component of marine environment represents the major sink for many radionuclides [3].It is widely known that the activities of these radionuclides in the sediment depend on the geological information, human activities and industries along the area.Thus, accumulation of these radionuclides in the sediment may raise many problems concerning safety of biotic life, food chain and ultimately humans [4].
Kuala Selangor is located in the Sungai Selangor estuary in the west coast of Peninsular Malaysia.Great development and various human activities in the west coast of Peninsular and along the river of Sungai Selangor released certain amount of radionuclide that will enter *Corresponding author at: E-mail address: zainihamzah@live.com(Zaini Hamzah) waterways and finally end up in the coastal area and marine environment.
A number of researches had been done at Kuala Selangor coastal area concerning of radionuclide concentration in water [5], sediment [6] and biota [7].However, no such data available that determine the activity concentration of natural radionuclide 226 Ra, 228 Ra and 40 K in surface sediment.
Hence, this study embark on determination of the activity concentration of natural radionuclide 226 Ra, 228 Ra and 40 K in surface sediment in sourthern Kuala Selangor coastal area specifically at 'Pantai Remis' and 'Pantai Jeram' area.Besides, this paper will also evaluate the radiological hazard due to this radionuclide by calculating the radium equivalent, absorbed dose rate, annual effective dose rate and external hazard index.This study is important to provide data on current radiation hazard and assessment of potential hazard in the future.

Sample collection
Sediment sample was taken manually using grab method at a depth of 10 centimetres from the surface along the coastal area and from the coastal area toward the sea during low tide on 13 January 2011 and 16-17 March 2011.All 14 surface sediment samples were collected from 14 sampling point.Seven sampling point was from 'Pantai Remis' area and another seven sampling point was from 'Pantai Jeram' area in sourthern Kuala Selangor coastal area as shown in Figure 1.Distance between each point is about 300-500 meter.The sampling point positions were determined using Global Positioning System (GPS).Table 1 shows the GPS coordinate and sampling location of the study area.

Sample preparation
The surface sediment samples were brought to the lab and dried in the oven at 60°C until constant weight.Then, it was grinded to fine powder using agate ball mill and sieve using 250 µm mesh-sieve.About 300-400 g of surface sediment was packed into polyethylene container and allowed the radionuclides to achieve secular equilibrium for at least 3 weeks prior to measurement using gamma spectrometry system.

Gamma spectrometry system
The activity concentration 226 Ra, 228 Ra, and 40 K were counted for 14400 s econds life time using gamma spectrometry system with ORTEC p-type HPGe coaxial detector coupled to a spectrum processing system.The HPGe has a r esolution of 1.85 keV and 25 % relative efficiency at 1332 keV 60 Co gamma-ray.The background radiation was also measured to carry out the necessary correction.Efficiency calibration of the spectrometer was carried out by using analytical grade UO 3 ore in KCl matrix prepared in the laboratory using identical container geometry as the samples.The spectrum processing and analysis were done using ORTEC GammaVision TM Version 6.07 software [8]. 226Ra activities were determined by taking the photopeaks of its daughter nuclides; 214 Bi at 609.3 keV.The 228 Ra activities in the samples were determined by measuring the intensity of 228 Ac at 911.1 keV.Meanwhile, the activities of 40 K were determined directly via its 1460 keV energy peak [9].

Activity concentration
The results for activity concentration of 226  Generally, the mean activity concentration of 226 Ra, 228 Ra and 40 K in 'Pantai Remis' and 'Pantai Jeram' are almost similar.Besides, the activity concentration of the study radionuclide is closely related to the human activities in the area as reported by many researchers [3], [10], [11], and [12].Human activities such as agricultural activities, mining operation and industrial processing ores may contribute to the enhancement of elemental composition in sediments and, in some cases; also increase the radionuclide concentrations [13].
Besides, Kapar coal power plant that located near to the sampling area may release some natural radioactivity due to the combustion of coal through atmosphere and consequently being absorbed into the sediment.As reported in [14], it is assumed that the higher activity of natural radionuclide in coastal area of Kapar is affected by coal burning activity.Fly ash from the power plant will disperse and accumulate in the sediment through rainwater fallout.  22Ra in southern Kuala Selangor is higher than coastal Sabah and Sarawak but slightly lower for 40 K [15].The mean value of 226 Ra is slightly higher than West Coast of Peninsular Malaysia (14.25-38.90)Bq/kg and the mean value of 228 Ra is within the range (16.91-97.18)Bq/kg as reported in [16].On the other hand, the mean value of 40 K is comparable with the study done in the East Coast of Peninsular Malaysia Exclusive Economic Zone (EEZ) (420 Bq/kg) and slightly higher for 226 Ra and 228 Ra [2].Nevertheless, mean concentration of 226 Ra and 228 Ra is comparable with the study done in Cubatao River, Brazil.In short, the activity concentration of 226 Ra, 228 Ra and 40 K in the study is area is quite close and comparable with other region in Malaysia as well as outside Malaysia .

Radiological assessment
Table 5 and Table 6 show the radium equivalent, absorbed dose rate, annual effective dose and external hazard index for 'Pantai Remis' and 'Pantai Jeram' area.
Radium equivalent activity, Raeq is used to estimate the hazard posed by different concentrations of radionuclides in materials, and is a measure on the suitability of a material to be used as building materials.The mean Ra eq for 'Pantai Remis' and 'Pantai Jeram' are 176.5 Bq/kg and 176.1 Bq/kg respectively.These values are lower than the adopted limit to avoid radiation hazard from the material that is 370 Bq/kg [17].
The mean absorbed dose rate for 'Pantai Remis' and 'Pantai Jeram' area are 82.72 nGy/h and 82.58 nGy/h.This value is higher than international recommended value which is 55 nGy/h [18].
The mean annual effective dose for 'Pantai Remis' and 'Pantai Jeram' are similar which is 0.101 mSv/y.The worldwide average annual effective dose is approximately 0.5 mSv/y [19].Thus, these values are lower than worldwide average.
The external hazard index for both 'Pantai Remis' and 'Pantai Jeram' is 0.484 which is less than 1.However, these values are higher than EEZ Peninsular Malaysia (0.38) [2] and East Malaysian marine sediment which is ranging between 0.17-0.33[18].

CONCLUSION
The mean activity concentration of 226 Ra, 228 Ra and 40 K in 'Pantai Remis' and 'Pantai Jeram' are almost similar.The activity concentration of study radionuclide is related to human activities in the surrounding area.
For 'Pantai Remis', the mean Ra eq is 176.5 Bq/kg.The absorbed dose rate is 82.72 nGy/h and annual effective dose is 0.101 mSv/y.For Pantai Jeram, the mean Ra eq is 176.1 Bq/kg.The absorbed dose rate is 82.58 nGy/h and annual effective dose is 0.101 mSv/y.The external hazard index for both 'Pantai Remis' and 'Pantai Jeram' is 0.484 (less than unity).Thus, it i s expected that no radiation hazard attributed to the radiation from the study radionuclides will be experience by people in the areas.

Table 1
GPS coordinate and sampling location of the study area.

Table 2
Activity concentration of 226 Ra, 228 Ra, and 40 K in Bq/kg in surface sediment sample taken from Pantai Remis, Kuala Selangor.The activity concentration of 226 Ra, 228 Ra and 40 K were compared with other study in other region as shown in

Table 4 .
The mean value of226Ra and

Table 4
Comparison of activity concentration of

Table 5
Radium equivalent, absorbed dose rate, annual effective dose and external hazard index for Pantai Remis area.

Table 6
Radium equivalent, absorbed dose rate, annual effective dose and external hazard index for Pantai Jeram area.