Health Risk Implications of High Background Radiation Dose Rate in Kampung Sungai Durian , Kinta District , Perak , Malaysia

Terrestrial gamma radiation dose rate measurement has been conducted around Kampung Sungai Durian (Kg. Sg.Durian), Kinta District, Malaysia. The mean value of outdoor terrestrial gamma radiation (TGR) dose rate and indoor inthe area are 458 nGy h-1 and 286 nGy h-1, respectively. It causes fatal cancer risk of about 9.90 x 10-5 per year to eachindividual. The activity concentrations of 238U, 232Th and 40K in soil samples were measured by gamma spectrometry. Itranged from 32 Bq kg-1 to 554 Bq kg-1, 64 Bq kg-1 to 1 806 Bq kg-1 and 21 Bq kg-1 to 2 522 Bq kg-1, respectively.Activity concentration of uranium and thorium ranged from


Introduction
A radiation survey was conducted throughout the State of Perak, Malaysia, to assess the environmental impact of amang deposits (amang being the local name for tin tailings that is a tin mining by product) (to be published).As a result of the survey, areas around Kg. Sg.Durian in the Kinta District of Perak, was identified as having the highest background radiation in the state.In the context of determining the significance of a critical pathway, an assessment on health physics implications of the high radiation dose in the area was carried out.The results obtained for this area can be used to determine the natural radiological status of Perak state and then be used as one of the baseline data in the assessments of the environmental impact of amang deposits in Perak State.
The concentration of uranium and thorium in high radiation area is associated with soil originating from igneous rocks (Kogan et al., 1969).Background terrestrial gamma radiation dose rate is influenced by soil type, geological feature and geographical condition (Florou & Kritidis, 1992;Ramli, 1997).
The world average values for terrestrial gamma radiation dose rate outdoor and indoor are 57 nGy h -1 and 75 nGy h -1 respectively (UNSCEAR, 2000).The highest concentrations of radioactive minerals in soil are found in Brazil and India (Radhakrishna et al., 1993).The abnormally high terrestrial gamma radiation in Brazil is due to the presence of monazite sand along the Atlantic coast and volcanic intrusion in the state of Minas Gerias.Dose rate in this area ranged up to 2.1 Gy h -1 (Malanca et al., 1993;Roser and Cullen, 1964;the Brazilian Academy of Science, 1977).
The study area as shown in figure 1 is located between the latitudes 4 o 15' to 4 o 21' North, and the longitudes 101 o 00' to 101 o 04' East (Director of National Mapping Malaysia, 1996).The area is situated in the South East of Kinta district, Perak, Malaysia.The climate is tropical with temperature between 28 o C to 32 o C. The area is 40 m to 70 m above sea level.It has a population of 1 643, within an area of 71 km 2 .Kampung Sungai Durian is underlying by two geological formations (Director General of Geological Survey, 1985) (i) Carboniferous, with limestone and sedimentary rocks in the western part, and (ii) Acid undifferentiated with igneous acidic rocks, these are mostly granitic rocks and are found in the eastern part.The soil types present according to FAO/UNESCO classification (Director General of Agriculture Peninsular Malaysia, 1973) are dystric histosols (peat), gleyic acrisols (Lunas), haplic acrisols (Rengam), ferric acrisols (Bukit Temiang) and disturbed land (urban and mining land).

Materials and Methods
The samples were taken randomly along the longitudinal and latitudinal grid line.Figure 2 shows Kg Sg Durian with its soil types and geological background and where the samples were taken.The measurement of terrestrial gamma radiation dose rate was done from September 2004 to April 2006.

Terrestrial gamma radiation (TGR) dose rates
The measurements were carried 1 m above the ground.The detector used was model 19, micro roentgen ( R) meter, manufactured by Ludlum, USA.It uses 1 × 1 (2.54 × 2.54 cm 2 ) sodium iodide (NaI) crystal doped with thallium (Tl).The instrument was calibrated by Malaysia Nuclear Agency; it is a Secondary Standard Dosimetry Laboratory (SSDL).The measurement indoor in concrete houses and outdoor for TGR dose rates were done on the same sites.The terrestrial gamma radiation dose rate measured from 270 outdoor locations and 70 indoor locations.For indoor measurement was done in living room, with 1 m from the surface and 1.5 m from the wall.Figure 3 shows a correlation between indoor and outdoor measurements, the linear correlation is good with R = 0.98.The Intercept of 114 on the y-axis indicates the presence of intrinsic gamma radiation from the building materials.

Soil, water and plant samples preparation
Twenty eight of soil samples were collected about 15 cm depth from the soil surface.The sample were dried by placing them in an oven at 110 o C for 24 hours then crushed and ground to fine powder by using a grinding mill (Herzog-D4500/type HSM 100, No. 62B/529, German-made).The samples were sieved by passing through a 200 mm test sieve/150 microns to be homogenized in size.Samples were placed and sealed in marinelli beaker for at least one month, before gamma spectrometric analysis, to ensure secular equilibrium (Mollah et al., 1987;Ibrahim et al., 1993).
Twelve of water samples were collected from ground water, fish ponds, stream, and river.Two liters of water from each sampling point was taken and filtered using 4.5 mm pore size filter paper to eliminate impurities from soil, plant, sandstone, and other materials.2 ml nitrite acid (HN0 3 ) was added to a liter of the sample, so that the water pH became less than 2 (IAEA, 1989).Water samples were evaporated by boiling to a volume of about 20 ml.continuing evaporated by boiling in a polyethylene vial to a volume about 2 ml for NAA analysis.
Fourteen of plant samples were collected from moss, tapioca, oil palm, banana, jack fruit, rambutan and water spinach.Distilled water was used to clean and remove soil contaminants to the plant samples.The samples were dried by placing them in an oven at 60 o C for 24 h.Their dry weights were determined.The samples were turned into ashes in a furnace at 450 o C for 24 h.The ashes were powdered and homogenized to a 0.2 g sample and packed in a polyethylene vial for NAA analysis

Samples analysis
Soil samples were prepared to determine 236 U, 232 Th and 40 K concentration by using gamma ray spectrometry with a coaxial high purity germanium (HPGe) detector.The radionuclide considered was determined the peak at 212 Pb (239 keV), 208 Tl (583 keV) and 228 Ac (911 keV) for 232 Th, the peak at 214 Pb (352 keV) and 214 Bi (609 keV) for the 238 U and the peak at 1 460 keV for 40 K.The standard samples IAEA SL-14 and IAEA SL-2 were used as reference materials and were mixed with SiO 2 in Marinelli beakers.For calibration, the IAEA reference materials 133 Ba, 22 Na, 137 Cs, 60 Co and 152 Eu, were used.The minimum detectable activity for counting time 10 800 s were estimated to be 4 Bq kg 1 , 9 Bq kg 1 and 19 Bq kg 1 for 238 U, 232 Th and 40 K respectively.
Plants and water samples were prepared to determine 238 U and 232 Th concentration by using NAA method in the TRIGA Nuclear Reactor available at Malaysian Nuclear Agency.Quality assurance and control procedure used have been described elsewhere Ramli et al., (2005).

Estimation of health risk.
To estimate the fatal cancer risk to an individual, i R .The equation below is used (Alvarez, 1997): Where a is the risk factor, that uses the value of 0.05 per sievert (public) for terrestrial gamma radiation dose (ICRP 1990), H Ein and H Eout are effective dose rates indoor and outdoor respectively.Dose factor for intake rate is 4.50 ×10 8 Sv Bq 1 and 2.30 ×10 7 Sv Bq 1 for 238 U and 232 Th respectively for adult members of the public (UNSCEAR 2000).

Results and Discussion
The terrestrial gamma radiation dose rate outdoor locations, ranged from 78 nGy h -1 to 1 039 nGy h -1 with the mean value of (458 ± 295) nGy h -1 , Figure 4 shows the isodose of terrestrial gamma radiation dose rate at Kg Sg Durian, Perak.This value is about 9 times the world average value of 57 nGy h -1 and 5 times the Malaysian average value of 92 nGy h -1 (UNSCEAR 2000).For indoor values, TGR dose rates were measured at 70 locations inside concrete houses, the value obtained ranged from 195 nGy h -1 to 390 nGy h -1 .For all data, using the indoor mean value was estimated to be (286± 95) nGy h -1 .The corresponding annual effective dose equivalent average for TGR dose rates indoor and outdoor are (1.39 ± 0.72) mSv and (0.59 ± 0.21) mSv respectively.The TGR annual effective equivalent dose for this area is 1.98 mSv that is 4 times higher than the reference value of 0.48 mSv (UNSCEAR 2000).This value, by using equation (1) cause fatal cancer risk of about 9.90 x 10 -5 per year to each individual in the area.
Table 1 shows the value of TGR dose rates from different soil types and geological features in the study area.The highest TGR dose rate outdoor of 1 039 nGy h -1 were found at locations with soil type haplic acrisols -ferric acrisols (Rengam Bukit Temiang) that originate mainly from granitic rock.The annual effective dose in the area with 100% outdoor occupancy is 6.37 mSv.This value will cause fatal cancer risk of about 3.19 x 10 -4 per year.
The gamma dose rates at soil sampling location involving different soil types and geological background are given in Table 2.The activity concentration for the 28 soil samples ranged of 32 Bq kg -1 to 554 Bq kg -1 , the mean value is (196 ± 43) Bq kg -1 for 238 U; 69 Bq kg -1 to 1 806 Bq kg -1 , with mean value of (628 ± 169) Bq kg -1 for 232 Th.; and 21 Bq kg -1 to 2 522 Bq kg -1 , with mean value of (475 ± 89) Bq kg -1 for 40 K.These values are higher than the world average as given by UNSCEAR.The most abundant radionuclide was thorium ( 232 Th).Thorium to uranium ratio is and thorium to potassium is 3.20 and 1.32 respectively, they are higher than reference value.The highest level of concentration was found in haplic-ferric acrisols (Rengam Bukit Temiang) soil type which originates mainly from granitic rock.
Table 3 shows the activity concentration of uranium and thorium in plants.The mean activity concentration of uranium and thorium in oil palms sample are (64 41) mBq kg -1 and (60 33) mBq kg -1 respectively.The mean activity concentration of uranium and thorium in leafy vegetable samples are (30 13) mBq kg -1 and (19 12) mBq kg -1 , respectively.The mean activity concentration of uranium and thorium in fruits samples are (3.7 1.8) mBq kg -1 and (2.1 1.5) mBq kg -1 respectively.Those values are higher than the reference values for uranium and thorium in leafy vegetables, fruit and grain (UNSCEAR 2000).If the annual consumption rates of oil palm, leafy vegetables and fruit respectively are used, which are 30 kg, 60 kg, and 170 kg, respectively, the resulting annual intake for uranium and thorium will be 1.9 Bq and 1.8 Bq in oil palm samples, 1.8 Bq and 1.1 Bq in leafy vegetables, and 0.6 Bq and 0.3 Bq in fruits, respectively.This will contribute to annual effective doses of 0.19 Sv and 0.74 Sv for uranium and thorium, respectively.The plant annual effective dose for uranium and thorium of 0.93 Sv is higher than the reference values of 0.63 Sv for adult (UNSCEAR 2000).The annual intake due to the consumption of plant is low.Activity concentration in plant contributes only insignificant small risk towards fatal cancer that is 4.7 x 10 -8 per year.Moss samples were collected for comparing uranium and thorium concentration with plant samples.Moss is a nonvascular plant and is a good absorber of uranium and thorium compared to other plants.Uranium activity in moss samples varies from 355 mBq kg -1 to 996 mBq kg -1 , and thorium activity varies from 464 mBq kg -1 to 1274 mBq kg -1 , with the mean value of (599 346) mBq kg -1 and (820 413) mBq kg -1 for uranium and thorium, respectively.These values indicated that moss is a more efficient absorber of uranium and thorium compared to oil palms, leafy vegetables and the fruit, as similarly reported by Say and Whitton (1983), Mouvet (1984), Tremolieres et al. (1994) and Ramli (2005) The concentrations of uranium and thorium in water samples are shown in Table 4.The mean activity concentration of uranium and thorium in all water samples is (9.6 7.0) mBq l -1 and (2.5 1.6) mBq l -1 respectively.These values are higher than the reference values of drinking water in the word of 1 mBq l -1 and 0.05 mBq l -1 for uranium and thorium respectively (UNSCEAR, 2000).The estimated annual intake of radioactivity due to the consumption of water is calculated using water ingestion rate of 500 l y -1 (UNSCEAR 2000).The value will contribute to annual intake of 4.8 Bq and 1.3 Bq for uranium and thorium, correspondingly.The annual effective dose for water sample is 0.21 Sv for uranium and 0.33 Sv for thorium.It will cause fatal cancer risk of about 2.70 x 10 -8 per year.

Conclusions
The mean natural terrestrial gamma radiation dose rate in Kg.Sg.Durian is about 5 times higher than the Malaysian average and about 9 times higher than the world average value (UNSCEAR 2000).The population does receive relatively higher background TGR exposures, however the increase in fatal cancer risk of about 9.90 x 10 -5 y -1 per capita is not high enough to cause for alarm.
The results indicate that the radionuclide contribution to annual effective dose rate from plant and water are higher than the reference values provided by UNSCEAR, nevertheless their contribution of 4.7 x 10 -8 y -1 for plant and 2.70 x 10 -8 y -1 for water per capita towards fatal cancer risk is relatively insignificant from health physics point of view.It might be a good policy to institute basic and simple radiological health monitoring for the affected area but probably nothing more than that.
The results obtained indicate that the most critical natural radiation area in Perak does not pose significant health physics risk, therefore the overall natural radiological status of Perak state is not out of norm.
United Nations Scientific Committee on the Effect Atomic Radiation.(2000).Sources and Effects of Ionizing Radiation.UNSCEAR Report 2000.

Figure 1 .
Figure 1.Study location at Kg Sg Durian, Malaysia

Table 1 .
Terrestrial gamma radiation dose rate from different soil types and geological background around Kg Sg Durian

Table 3 .
Concentration of uranium and thorium in plant samples (dry weight)

Table 4 .
Specific activity of uranium and thorium in water samples