Depth Profile of 137 Cs Fallout in Soil in Cameron Highlands

Cs is one of the important man-made radionuclide introduced into the environment through nuclear weapons testing and nuclear accidents. In Cameron Highlands meaningful activity concentration of Cs radionuclide has been measured. The present study embarked on the determination of Cs activity concentration in soils of the sloping area. This would enable the distribution profile in the soil be investigated. Soil profile samples were collected by using scrapper plate in the sloping area which covers top, centre and bottom of the hills and a core in the forest for comparison purpose. The scrapper is 40 cm long and able to obtain slice of 2 cm interval of soil with diameter of 15.2 cm. Soil samples were oven dried, ground, sieved, homogenize and seal properly into a plastic container. The Cs activity concentration was measured by using low background coaxial hyper pure germanium detector gamma spectrometer based on Cs 661.66 KeV gamma ray. Results showed there were trend of low activity on the top of the hill and subsequently increases downhill. In all location, two trends of profiles were observed starting from the depth of 0 cm to 18 cm and 18 cm to 30 cm which indicating the presence of two sources of Cs. The Cs activity concentrations range detected at top location was from 0.05 Bq/kg to 1.53 Bq/kg, centre was 0.22 Bq/kg to 2.11 Bq/kg, bottom was from 0.00 Bq/kg to 2.03 Bg/kg and forest was 0.00 Bq/kg to 0.96 Bq/kg. The basic parameters of the soil such as pH (top; 3.72, centre; 4.26, bottom; 4.02), density (top; 1.45 g/m, centre; 1.41 g/m , bottom; 1.59 g/m ) and organic matter content (top; 17.08 %, centre; 16.75 %, bottom; 20.32 %) also being tested. These results show that the relative activity concentration of Cs at the top is lowest, while at the bottom is highest, representing the presence of downward transport. However, identical pattern of profiles were observed at the three points of the slopes. | Depth Profile | Cs method | Gamma Spectrometer | Cameron Highlands | ® 2012 Ibnu Sina Institute. All rights reserved. http://dx.doi.org/10.11113/mjfas.v8n1.118


INTRODUCTION
Cs has been introduced into the environment as a result of nuclear bomb tests and nuclear power plant accidents [1].Bomb-derived 137 Cs has been used to document soil degradation in different environment of northern and southern hemispheres.An additional input of Chernobyl-derived 137 Cs from Chernobyl accidents in 1986 was superimposed on the bomb-derived 137 Cs pattern within eroded areas.Based on the field measurement, there is a similarity of the depth distribution of bomb-derived 137 Cs with Chernobyl-derived 137 Cs for the main soil type [2].Due to its relatively long physical half-live (30.2 years) and bioavailability, 137 Cs is one of the great concern fission products [3].It is also has a long residence in the environment and is a hazard if found in sufficient concentrations [4].Cesium is an alkali metal with chemistry similar to that of sodium, potassium and other elements in group 1 in the periodic table [5].Much of the success of 137 Cs as a tracer is attributable to its low solubility and its ability and readily absorbs to small soil particles.
The positive charge fallout cesium ( 137 Cs + ) once reaching the earth surface is readily adsorbed onto the cation *Corresponding author at E-mail addresses: zainihamzah@live.com(Zaini Bin Hamzah) exchange sites on the surface soil particles and remains in this state almost in all terrestrial environments [6].The raise used of artificial radionuclide 137 Cs in the current year has been seen by geomorphorlogists and soil scientist in determination of patterns and rate of soil redistribution [7].137 Cs contamination is positively correlated with altitude, so the upland, most susceptible sites, is ironically mostly contaminated too [8].The significant of 137 Cs study in this area could provide the baseline data since not many studies in this research field in Malaysia.This paper presents the study of 137 Cs activity concentration in the soil, identifying distribution pattern of soil and comparing the 137 Cs depth profile in a hill of agricultural area and forest in Cameron Highlands, Pahang

Study Area
The study area is located in Cameron Highlands, Pahang.Its forms the smaller district located at North West of Pahang in the upper left corner inside the Pahang state.The place is situated on the main mountain range of Peninsular Malaysia [9].Cameron Highlands counts roughly 71,000 hectare of lands form which 79 percent is still forested which makes 21 percent developed.The specific study area was in agricultural area where it is the second major land used after forestry with 16.4 percent of the total land area [9].It is one of the areas with high altitude in Malaysia thus; the chance to receive fallout of 137 Cs radionuclide is relatively high.Figure 1 showed the sampling points in the study area.The details information on sampling locations using global positioning system is shown in Table 1.

Sampling and Sample Preparation
Soil samples were collected in sloping agricultural hill area (top, center and bottom) and in the forest namely PT, PC, PB and FR respectively.For each of the sampling point, bulk and depth incremental soil samples were taken.The scrapper plate with PVC pipe 40 cm long and 15.2 cm diameter was used for depth profile samples while a bulk samples were collected using hand auger with 20 cm long for basic parameter tests.The samples were taken to the laboratory for oven dried at 60 o C until constant weight, then ground using Fritsch pulverizes (400 rpm rotational speed, 2 repetitions, 5 minutes) and sieved through 250 µm sieve.A 150 g of samples was kept and sealed properly in the plastic container with diameter of 6 cm and 4 cm height.Table 1 The locations of the soil samples (composite and profile)

Measurements
Gamma spectrometer measurement was carried out using low background hyper pure coaxial germanium (ptype) detector.It is linked to a multi-channel digital analyzer system from EG & G, ORTEC.The gamma peak resolution at 1332 keV 60 Co was 1.82 keV and relative efficiency of 25 % with energy range from 40 keV to 10 MeV.The ORTEC Gamma Vision TM Version 6.07 software was used for the spectra analysis and processing [10].All the samples were counted at 28800 second live time and the spectrum was analyzed using Gamma Vision software for The minimum detectable activity (MDA) of this low background gamma spectrometer at 661.66 keV was 0.03927 Bq/kg calculated using the equation 2 [11]; (2)

N = background count T = counting time E = counting efficiency
The basic parameters cover pH, density (bulk density), texture (pipette method) and organic carbon content (loss of ignition) were also being tests.In-situ measurement using radiation survey meter (LUDLUM rate meter, Geiger Mueller Counter, model 2241) was record in each sampling location to determine radiation dose level.

Cs
The vertical distribution profile of 137 Cs for the study area is showed in Table 2.0.The activity concentrations of 137 Cs are observed low in the upper land and high in the bottom area.The accumulation of this radionuclide clearly showed in this sloping area, where there is a movement of 137 Cs from the upper site down to lower placed.This reflects the progressive accumulation of soils contains 137 Cs at the bottom of the slope [12].This result agrees with the surface dose reading as shown in Table 3.0.The surface dose reading at bottom of hill has higher the reading as compared to the center and top location.The depth profiles of 137 Cs activity concentration in the overall distribution patterns were observed and it seems to have the similar pattern.For the top, center and bottom of the slope, 137 Cs activity concentrations were slightly high in the top layer (0 cm to 2 cm) compare to inner layer of the soil profiles.
The 137 Cs activity concentrations decrease until 18 cm layer profile.The activity concentrations have increased again when reaching the depth of 20 cm and slowly decrease again down to 30 cm depth.These two trends indicate the presence of two different sources.The first trend of 137 Cs vertical profile may came from Chernobyl nuclear power plant accident in April 1986 [13].The second trend came from environment as a consequence of above ground nuclear weapon testing between 1945 to 1963 [5] as shown in Figure 2.0 to Figure 5.0.The mean value of depth profile 137 Cs activity concentrations at TP, TC, and TB were 0.73 Bq/kg, 1.22 Bq/kg and 1.32 Bq/kg respectively.
In the forest soils, most 137 Cs survive in the organic layer and migrated downward through leaching of 137 Cs in the forest floor in a very slow processed [14].The first layer of the forest soil was taken after removing the leaves and humus layer which cover the surface of the soil.For the first layer up to 16 cm, the 137 Cs activity concentrations decreased gradually.The second trend started at the depth of 18 cm.Decrease of 137 Cs in the first cm can be due to soil loss or 137 Cs migration in the soil matrix and animal perturbation [15].It is very low migration depth of 137 Cs in forest soil and even many decades after deposition the majority of 137 Cs activity concentration is retained in the surface organic soil layers [13]. 137Cs is attributed especially in the forest floor layers and the migration towards mineral horizons is function of mineralization of humus substances [13].Further information regarding this result can be supported by the basic parameters of soil as presented in Table 4.
Soil pH affects all chemical, physical and biological soil properties.Number of researchers has studied in soils, showed that variations in soil pH were natural, due to chemical characteristics of different type of soil [16].The results of soil samples analysis show that the pH of all samples is less than 5 (pH<5) i.e. within the range 3.18 -4.16.It has the trend that higher altitude showed lower soil pH as compared to the bottom part of the hill.Lower pH will help 137 Cs ions to move freely and easy being washed by the runoff water.Furthermore, the soil density (1.0 g/m 3 ) and porosity especially in the undisturbed area of the forest together with its soil composition has contributed to the adsorption of 137 Cs.
These indicate no human activities in the high elevation area compare in the bottom area (density 1.59 g/m 3 ).If the bulk density becomes too high, it can limit plant root growth.The specific bulk density that will adversely affect plant root growth and development depends on many factors including parent materials, soil texture, the crop being growth and management history [17].Soil texture in the hill location is sandy clay loam soil particles.Soil texture directly affects the porosity of soil, which in turn, determined its water-retention, flow characteristic and nutrient-holding capacity.Heavy clay soils normally have higher percentage of smaller pores and higher water holding capacity.On the other hand, sandy soils have relatively higher percentage of larger pores with lower water holding capacity under relatively dry conditions [18].

CONCLUSION
The activity concentrations of 137 Cs in soil for PT, PC, PB and FR shown the similar trend i.e. two depth redistribution trends.The obviously trends observed represent the first trend which indicating the sources from Chernobyl accident in 1986.While the second trend indicating the nuclear weapon test sources during 1950's to 1970's.This conclusion was supported by the basic soil parameters.The next stage of this study aim to cover more study area in this agriculture area thus will have complete set data and finally the soil erosion study can be done.

Fig. 1
Fig. 1 Google maps of the study location in the agricultural area.Inserted map shows the state of Pahang, Malaysia.

Figure 2 . 0 :Figure 3 . 0 :Figure 4 . 0 :Figure 5 . 0 :
Figure 2.0: Depth distribution of 137 Cs in top of the hill [10] at 661.66 keV of137Cs.The efficiency calibration of the detector was made using secondary standard made up of UO 3 and KCl matrix in the same geometry as the sample[10].The spectrometer efficiency at 661.66 keV obtained was used to calculate the activity concentration of 137 Cs in the soil using the equation,   = Mass in  of the measured sample energy

Table 2 . 0 :
Activity concentrations of137Cs at the slope of the hill and the forest

Table 3 . 0 :
Surface dose reading on the hill slope and the forest

Table 4 . 0 :
Basic parameter of soil samples in hill location and forest