Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia

EI-03561; No of Pages 11 Environment International xxx (2017) xxx–xxx

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Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia M.S.M. Sanusi a, A.T. Ramli a, W.M.S.W. Hassan a,⁎, M.H. Lee b, A. Izham a, M.N. Said c, H. Wagiran a, A. Heryanshah d a

Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, Skudai, Johor Bahru, Malaysia Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, Skudai, Johor Bahru, Malaysia Department of Geoinformation, Faculty of Geoinformation and Real Estate, Universiti Teknologi Malaysia, Skudai, Johor Bahru, Malaysia d Institute of Environmental & Water Resource Management, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Johor Bahru, Malaysia b c

a r t i c l e

i n f o

Article history: Received 8 September 2016 Received in revised form 23 December 2016 Accepted 12 January 2017 Available online xxxx Keywords: Soil pollution Ex-tin mine Radioactivity Gamma radiation exposure Lifetime cancer risk

a b s t r a c t Kuala Lumpur has been undergoing rapid urbanisation process, mainly in infrastructure development. The opening of new township and residential in former tin mining areas, particularly in the heavy mineral- or tin-bearing alluvial soil in Kuala Lumpur, is a contentious subject in land-use regulation. Construction practices, i.e. reclamation and dredging in these areas are potential to enhance the radioactivity levels of soil and subsequently, increase the existing background gamma radiation levels. This situation is worsened with the utilisation of tin tailings as construction materials apart from unavoidable soil pollutions due to naturally occurring radioactive materials in construction materials, e.g. granitic aggregate, cement and red clay brick. This study was conducted to assess the urbanisation impacts on background gamma radiation in Kuala Lumpur. The study found that the mean value of measured dose rate was 251 ± 6 nGy h−1 (156–392 nGy h−1) and 4 times higher than the world average value. High radioactivity levels of 238U (95 ± 12 Bq kg−1), 232Th (191 ± 23 Bq kg−1,) and 40 K (727 ± 130 Bq kg−1) in soil were identified as the major source of high radiation exposure. Based on statistical ANOVA, t-test, and analyses of cumulative probability distribution, this study has statistically verified the dose enhancements in the background radiation. The effective dose was estimated to be 0.31 ± 0.01 mSv y−1 per man. The recommended ICRP reference level (1–20 mSv y−1) is applicable to the involved existing exposure situation in this study. The estimated effective dose in this study is lower than the ICRP reference level and too low to cause deterministic radiation effects. Nevertheless based on estimations of lifetime radiation exposure risks, this study found that there was small probability for individual in Kuala Lumpur being diagnosed with cancer and dying of cancer. © 2017 Elsevier Ltd. All rights reserved.

1. Introduction Kuala Lumpur is one of the densely populated places in the world with a population density of over 6500 km− 2 (EPU, 2016). For the past few decades, Kuala Lumpur has experienced rapid urbanisation, from a tin-mining town to national capital (Hamzah and Hassan, 1996). However, rapid infrastructure developments, i.e. expansion of new township, residential area and industrial in Kuala Lumpur (Bahrin, 1981) have altered the earth landscapes, particularly soil bodies. Uncontrolled soil exploitation for development purposes can cause irreversible damage to environmental sustainability, especially on geochemical grounds (Peña-Fernández et al., 2014). Numerous concerns have been raised over the issues of effects of contaminants and ⁎ Corresponding author. E-mail address: saridan@dfiz2.fs.utm.my (W.M.S.W. Hassan).

heavy elements in soils due to urbanisation, industrialisation and traffic (Zhang et al., 2005). This scenario is exacerbated with the utilisation of former tin mining areas or heavy mineral- and tin-bearing alluvial soil in Kuala Lumpur. During constructions, i.e. dredging and reclamation practices could have technologically enhanced naturally occurring radioactive material (TENORM) in the soil and subsequently increase the existing background gamma (γ) radiation exposure. Generally, tin mining activities and former mine lands (e.g. tin tailings) in Peninsular Malaysia have been identified to pose adverse impacts on human radiological health and environment as a result of high γ radiation exposure and radioactivity contamination of 238U series, 232Th series and 40K in soil (Subramanian, 1988; AELB, 1991; Udompornwirat, 1991; Hewson, 1996; Roberts, 1995; Bahari et al., 2007; Bahari et al., 2007; Yasir et al., 2007). In fact, the government initiatives to conserve the environment sustainability and rehabilitation of ex-tin mines in Selangor and Kuala Lumpur are through the

http://dx.doi.org/10.1016/j.envint.2017.01.009 0160-4120/© 2017 Elsevier Ltd. All rights reserved.

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

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development of new townships, housing estates, and recreational park (Hamzah and Hassan, 1996; Ang and Ho, 2004; Yap, 2007). In addition, it had been reported previously in the early-90s that a large amount of cheap rock aggregate, tin tailing sand and clay from the ex-tin mines were supplied as construction materials for infrastructural development in Kuala Lumpur and nearby districts of Selangor (Hamzah and Hassan, 1996; Yap, 2007). Besides tin tailing construction materials, the utilisation of basic construction materials, i.e. granite aggregate, sand, red and white clay brick, cement brick and cement in construction site also could pollute the soil with the radioactivity of 238U series, 232Th series and 40K. Numerous worldwide studies (Chong and Ahmad, 1982; Mustonen, 1984; Ibrahim, 1999; Lee et al., 2001; UNSCEAR, 2000; Yasir et al., 2007; Trevisi et al., 2012; Ali, 2012; Ravisankar et al., 2012; Lu et al., 2014) found that the radioactivity concentrations in the construction materials have increased the indoor γ radiation exposure. Ibrahim (1999) reported that the radioactivity concentrations for 238U, 232Th and 40K in the red clay brick samples from Malaysia were 241, 51 and 7541 Bq kg− 1, respectively, whereas for the concrete samples were 51, 23 and 832 Bq kg− 1, respectively. For granitic aggregate sources, Zakaria et al. (1993) reported that the average concentrations of 238U, 232Th and 40K in granite samples from The Main Range Granite in Peninsular Malaysia were 314, 221 and 1315 Bq kg−1, respectively. These values are higher than the world's average concentration values (33, 45 and 420 Bq kg−1) of 238U, 232Th and 40K in soil (UNSCEAR, 2000). To date, no available data or studies particularly related to environmental radioactivity and radiological impact assessment due to urbanisation have been carried out in Kuala Lumpur. Globally, most of the studies involved only measurements of indoor γ radiation exposure and radioactivity of radon and thoron gases in dwellings (Niewiadomski et al., 1985; Saito et al., 1997; Amrani and Tahtat, 2001; Righi and Bruzzi, 2006; Trevisi et al., 2012; Lu et al., 2014). In 2010, a comparative study of indoor radon levels between Kuala Lumpur and Kerala, India was conducted by Mahat et al. (2011) to investigate the relationship between highly distributed heavy mineral areas and radon concentrations in dwellings. However, the study is localized, small sampling and not implying the outdoor radiation exposure and soil radioactivity in Kuala Lumpur. This study is conducted to assess the impact of urbanisation on background γ radiation in Kuala Lumpur. The main approaches used in this study is based on measurements of outdoor γ radiation dose rate and radioactivity concentration level in urban soil. Statistical analyses of ANOVA, t-tests and cumulative probability plots are adopted in this study to statistically verify the dose enhancements due to urbanisation impacts. The statistical verification techniques used in this study are mainly based on statistical hypothesis tests of comparison of background dose rate for similar geological features in Kuala Lumpur and other states. The cancer risk is estimated to assess the probability of hazard of ionizing radiation attributable to urbanisation impacts. The obtained baseline data are important for radiological protection and safety, radioactive contamination and waste control enforcement, and for formulating policies related to occupational and public safety due to nuclear energy practices. 2. Experimental materials and methods

Fig. 1. Geological map of the study area.

24% of the total land area. Fig. 2 shows the land use map of Kuala Lumpur (DBKL, 2016). The study area also involved few areas of former tin mines. Historically, tin ore in Kuala Lumpur was started mined in Ampang in 1857 (Tan, 2005). Roughly 30–50% of the world's annual tin production in the mid-1960s were majorly produced from two major tin ore resources in Malaysia (Hails, 1976), i.e. Kinta Valley (Perak) and Klang Valley (known as Kuala Lumpur and nearby districts in Selangor) (Wong, 1970; Tan and Ibrahim, 1990; Schwartz et al., 1995; Hamzah and Hassan, 1996). Fig. 3 shows the distributions of former tin mines in Kuala Lumpur (DMM, 1980). Note that not all tin mining areas in

Table 1 The geological backgrounds in Kuala Lumpur (Ingham and Bradford, 1960; DGSM, 1985). Geological background

Age of formation Compositions (1 × 106 y)

Carboniferous 350

2.1. Study area The study involved an area of 243 km2 of Federal Territory of Kuala Lumpur. Kuala Lumpur comprises 3 geological background, i.e. carboniferous, Silurian-Ordovician and granite acid intrusive. The geological map of Kuala Lumpur is shown in Fig. 1 and the information of their formation ages as well as types of rock are summarised in Table 1. Kuala Lumpur terrain area consists 89% disturbed land, i.e. township sites (DAPM, 2002). Meanwhile, according to the land use report in 2000 (DBKL, 2016) the undeveloped land in Kuala Lumpur was about

SilurianOrdovician

435

Acid intrusive N500

Known as the Kenny Hill formation, comprises significant interbedded quartzite and phyllite. The sedimentary rocks of Kenny Hill formation i.e., shale and sandstone have been regionally metamorphosed into metasediments i.e., schist, quartzite and phyllite. The region is underlain by the alluvial soil (heavy mineral and tin-bearing soil). Locally prominent development of limestone, called the Kuala Lumpur Limestone. Most of the limestone formations have been metamorphosed into marble. Locally known as the Kuala Lumpur granite. Consists of medium coarse, porphyritic muscovite-biotite granite.

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

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to-dose rate conversion unit in linear equation (Eq. (1)) below (Ramli et al., 2016): D ¼ B  J  C f  8:7 nGy μR−1

ð1Þ

where, calibrated dose rate was denoted by D (nGy h−1) whilst, the survey meter output reading (in exposure rate) was denoted by B (μR h−1). J represents the correction factors for each range of exposure rate. The values of J were 1.00, 1.03 and 0.96 for exposure rate range of 0–5000 μR h−1; 0–500 μR h− 1 and 0–250 μR h−1, respectively. Cf represented the calibration factor for measured exposure rate from survey meter output reading, B. Cf is defined as conventional true value of primary or secondary standard sources (e.g., 137Cs; 662 keV or 60Co; 1250 keV) divided by indicated value from instrument reading. The calculated Cf values in this study for 137Cs and 60Co were 0.95 ± 0.05 and 1.49 ± 0.03, respectively. For calibration purpose, the average value of Cf i.e., 1.22 ± 0.27 was used in Eq. (1). The value of 8.7 nGy μR−1 was applied for conversion unit of exposure-to-dose (micro-Roentgen to nano-Gray). 2.3. Gamma spectrometry analysis for 238U, 232Th and 40K

Fig. 2. Land use map of Kuala Lumpur in 2000 (DBKL, 2016).

Kuala Lumpur are indicated in this map. Owing to the Second World War, most of the recorded information concerning the tin mining areas in Klang valley were lost or destroyed during the war (Tan, 2005). 2.2. Gamma dose rate survey Kuala Lumpur territory was divided into squares of area of 1″ longitude × 1″ latitude (~1.86 km × 1.84 km). The locations of survey were randomly selected within the grid cell (~3.4 km2), by considering accessible areas, open and flat terrestrial space, away from outcrops, roads, pavements and any concrete foundations. Fig. 3 shows the sampling points in the study area. Initially on each sampling location, 4 measurements of exposure rate were taken at different spots, about 5–10 m apart to test the local variability of measurements. Subsequently, they were averaged to obtain the best value that represents the exposure reading of the place. The measurements were taken at 1 m above the flat soil surface using scintillation survey meter model 19, Micro R meter manufactured by Ludlum Measurement, U.S.A (Ludlum, 1993). The range of energy detection of the instrument covers almost the significant primordial γ radiation emitters (Ramli et al., 2003) including the anthropogenic γ emitter 137Cs (661.7 keV) (Ludlum, 1993). The instrument has low detection limit of energy, approximately 60 keV. The energy calibration of the instrument was carried out using standard multi-nuclides of 241Am, 57Co, 133Ba, 137Cs, and 60Co (Ludlum, 1993). The energy calibration has produced a non-linear energy response curve ranged from 59.54 keV–1.17 MeV. As the instrument is NaI (Tl) based detector, it over-responds to scattered and low energy photons thus, overestimating the actual values of ambient dose. In order to overcome this, the instrument was experimentally calibrated at the Secondary Standard Dosimetry Laboratory (SSDL) in the Malaysian Nuclear Agency. This was performed at different exposure ranges of 0–5000 μR h− 1, 0–500 μR h−1 and 0–250 μR h− 1. The instrument calibration was expressed in term of dose rate by applying exposure-

In order to identify the main sources of the measured γ radiation, soil samples were retrieved in the study area for γ spectrometry analysis of radioactivity concentrations. 16 top soil samples were randomly taken at dose measurement locations to represent the urban soil. Top soil samples were consistently taken at a depth of 20 cm–25 cm to avoid taking any mature and well-developed soils that would have represented geological background of Kuala Lumpur. The samples were dried, crushed and sieved through 2 mm mesh-sized sieve to obtain homogenous sizes of soil particulates. The samples were tightly sealed in marinelli beaker using an adhesive tape and left for one month to achieve equilibrium between the progeny in the 238U series and 232Th series. All the samples were analysed using gamma spectrometry. The gamma spectrometer was equipped with a 7.6 cm (diameter) × 7.6 cm (height) cylindrical detector of coaxial high-purity germanium (HPGe). The relative efficiency of the detector is 20% at a photon energy of 1332 keV for a Co-60 point source. The detector provided 1.8 keV resolution and was calibrated with the 1332 keV energy peak from a Co-60 point source and the detector's energy calibration was made using the same point source. The gamma spectrometry system was also equipped with a nitrogen based cooling system, preamplifier electronic unit, Genie 2000 VI.3 analysis software and lead shielding. For efficiency calibration, the gamma spectrometer was calibrated using 500 ml multi-nuclide standard sources of 210Pb, 241Am, 109Cd, 57 Co, 123mTe, 51Cr, 113Sn, 85Sr, 137Cs, 88Y and 60Co (internal reference of standard sources provided by Eckert & Ziegler Isotope Products; source no.: 1232-2) distributed in a soil matrix. The concentration of 238U was obtained by determining the γ energy peaks of 214Pb and 214Bi, whereas 208 Tl and 228Ac were used for 232Th and the γ-energy peak of 1460.8 keV for 40K was used directly (IAEA, 1989). By considering the net area under the energy peak NEi at energy E, mass of the soil samples Ms, gammas per disintegration Pγ of the progenies at peak energy E, counting time t, and peak detection efficiency εEi at peak energy Ei, the activity AEi concentration for each radionuclide (Bq kg−1) was calculated using the following formula (IAEA, 1989); AEi


 ¼ NEi ∕ εEi  t  P γ  M s

ð2Þ

2.4. Statistical analysis using ANOVA and t-tests for dose rate comparison To test the significant difference between the mean of two or more variables the F-ANOVA is used. At confidence level α and degree of freedom df, the null hyphothesis Ho: μ1 = μ2, is rejected if the F-ratio N

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

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Fig. 3. Locations of sampling point and former tin mining areas.

F-critical (Fα, (2, n − 2)). The empirical method to calculate the F-ratio is given by (Weiss, 2008): F¼

MST MSE

2

∑i¼1 ni ðμ i −μ Þ2 ¼2 3  2 ∑i ∑ j μ ij 2 6 7 2 −∑i¼1 ni ðμ i −μ Þ 5=n1 þ n2 −2 4∑i ∑ j μ ij 2 − n1 þ n2

ð3Þ

to identify which geological types that differs from the others, the 2 tail t-test was used. For two-samples assuming unequal variances, the value of t-statistic was computed using following equation; μi− μ j t−stat ¼ vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi !ffi u u Si 2 S j 2 t þ ni nj  Degreesoffreedom; df ¼

where, μ is the mean value for sample dose rates μ of sample populations j = 1, 2, 3,…., nj and i = 1, 2, 3…., ni. MST is a mean sum of squares due to treatment and MSE mean sum of squares due to error in ANOVA analysis. The ANOVA analysis was computed using PASW 19 SPSS software. ANOVA results only show the degree of significance between means of two or more variables and do not indicate which groups or variables differ from each other. In order

ð4Þ

Si 2 ni

1 S2i ni −1 ni

!2

S2

2

þ n jj S2j 1 þ n j −1 n j

!2

ð5Þ

where, S denoted as sample variance for both population i and j. At a confidence level α/2 = 0.25 and df, the null hyphothesis of Ho: μ1 = μ2, is rejected if the t-stat b − t-critical two tail (tα/2, df) or t-stat N t-critical two tail (tα/2, df) (Carver and Nash, 2000).

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

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Table 2 Descriptive statistics for the dose rate survey in Kuala Lumpur based on geological information. Statistical parameter

n Mean ± standard error Range Confidence interval of mean (95%) World average (UNSCEAR, 2000)

γ radiation dose rate (nGy h−1) Granite acid intrusive

SilurianOrdovician

Carboniferous

Total

17 278 ± 12 226–392 252–303

34 244 ± 8 156–348 227–261

20 239 ± 10 174–348 217–260

71 251 ± 6 156–392 239–262

–

–

–

59

3. Result and discussion 3.1. Evaluation of enhancement of background radiation exposure A total of 71 measurements of dose rates were measured throughout Kuala Lumpur and the results of descriptive statistic based on geological features are presented in Table 2. The mean values of measured dose rate for granitic, Silurian and Carboniferous contexts in Kuala Lumpur show high values exceeded 200 nGy h−1. The confidence intervals of mean indicates that 95% confident of measured dose in granitic, Silurian and Carboniferous regions will show high dose rate i.e., between 253– 303, 227–261 and 217–260 nGy h−1, respectively. Many previous studies have revealed the influences of geological setting on background radiation (Quindós et al., 1991; UNSCEAR, 2000; Tzortzis et al., 2003; Ramli et al., 2003). Sanusi et al. (2014) has statistically verified that granitic is the main factor to high contribution of background radiation (N 250 nGy h−1) in state of Selangor, whereas, low background radiation (b190 nGy h− 1) are mostly associated with metamorphic and sedimentary based rocks (UNSCEAR, 2000) from Silurian to Carboniferous age e.g., limestone, shale, sandstones, schist, quartzite and phyllite (DGSM, 1985). Similar findings were also reported by Lee et al. (2009) and Almayahi et al. (2013) for Kinta district (Perak state) and the Northern States, respectively. Table 3 shows the comparisons of mean value of dose rate between the states based on geological features. The mean values for Silurian and Carboniferous in Kuala Lumpur are relatively higher compared to other states, whilst for granitic, all states indicate almost similar mean values i.e., exceeded 250 nGy h−1 except for Northern states which is slightly low i.e., 212 ± 10 nGy h−1. Further analysis was performed based on visual interpretation of data dispersion (i.e., boxplot) using data sets of each state. For Silurian and Carboniferous, Fig. 4 visually shows sharp distinctions of mean values (+ sign) and interquartile range boxes (IRQ) (coloured box represents 50% of data) between Kuala Lumpur and other states. Meanwhile for granitic, no noticeable differences of mean values and IRQ boxes between Kuala Lumpur and other states except for Northern states which slightly lower than other states. High mean values of dose rate in granitic region indicated by Kinta district (Perak) and Selangor are influenced by few outlier points and extreme outliers of up to 700 nGy h−1 (points and asterisks symbol in Fig. 4), which elevating their mean values comparable to Kuala Lumpur. Few localities of high dose level indicated by these outliers are due to highly distributed radium contents in soil at the granitic mass, e.g., Kampung Sungai

Fig. 4. Analysis of data dispersion (Boxplot) based on different geological regions and states.

Durian (Ramli et al., 2009) and Genting Highlands, Selangor (Sanusi et al., 2014). Moreover, high mean values indicated by the granitic regions of Kinta district (Perak) and Selangor are relevant, as previously stated that Kinta Valley (Perak) was once the largest tin-ore deposits in Malaysia and few districts of Selangor nearby Kuala Lumpur are part of the areas of Klang Valley tin deposits. Meanwhile, based on evaluation of data tendency as shown by the whisker of boxplot in Fig. 4, both of low and high whiskers (represents 90 % of total data) for granitic region of Kuala Lumpur are situated between 226 and 392 nGy h−1, whilst for Northern States, Kinta district (Perak) and Selangor are between 150–250 nGy h−1, 50–500 nGy h−1, and 150–400 nGy h−1, respectively. This infers that there is high certainty that dose rate measurements in granitic region of Kuala Lumpur will indicate high doses and deviate less compared to other states. Large dispersions of dose rate indicated by Kinta district (Perak) and Selangor are mainly due to minor cases of measurements which indicated low doses in granitic regions. Based on mean comparisons in Table 3 and boxplot analyses, these are the evidences of an enhancement of the dose rate above the natural background in Kuala Lumpur. The enhancements of background dose rate in Kuala Lumpur due to urbanisation impacts are only noticeable for Silurian and Carboniferous regions whereas for granitic region, the enhancements of background dose rate are not significant. The only notable difference of mean values between the states, for granitic regions, is indicated by Kuala Lumpur and Northern states. Nevertheless, in terms of tendency of dose range it can be concluded that there is significant certainty of higher dose range in granitic region of Kuala Lumpur compared to other states. 3.2. Statistical verification of dose enhancement in urban areas Table 4 shows that the calculated statistical F-value (1.396) is less than F-critical (2.631), which indicates that there are no significant differences between the mean values of dose rate measured in granitic regions of all states. This confirms the comparisons made in Table 3

Table 3 Descriptive statistics of dose rate survey in Kuala Lumpur, Selangor, Perak and Northern States based on geological features. State/federal territory

n

Kuala Lumpur Selangor Perak (Kinta district) 1 Northern states

71 35 396 15

Mean ± standard error (nGy h−1)

References

Granite acid intrusive

Silurian-Ordovician

Carboniferous

278 ± 256 ± 285 ± 212 ±

244 ± 184 ± 169 ± 132 ±

239 ± 10 151 ± 6 87 ± 10 124 ± 4

12 16 6 10

8 18 7 39

This study Sanusi et al., 2014, 2016b Lee et al., 2009 Almayahi et al., 2013

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

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Table 4 Anova single factor for mean comparison of dose rate based on granitic parent material in 4 states. Source of Variation

SS

df

MS

F

P-value

F-crit

Between groups Within groups Total

43135.49 3562513.00 3605649.00

3 346 349

14378.50 10296.28

1.40

0.24

2.63

Table 5 t-test two-samples assuming unequal variances for mean comparison of dose rate based on metamorphic and sedimentary parent material in 4 states. Paired-variables

t-stat

t-critical two-tail

Conclusion (95% confident interval)

Kuala Lumpur – Selangor Kuala Lumpur – Perak Kuala Lumpur – Northern States

2.95 9.53 11.59

2.10 1.98 2.03

Rejected Ho Rejected Ho Rejected Ho

Table 6 Anova single factor for mean comparison of dose rate based on metamorphic and sedimentary parent material in 3 states (Selangor, Perak and Northern states). Source of Variation

SS

df

MS

F

P-value

F-crit

Between Groups Within Groups Total

20757.43 479123.06 499880.49

2 117 119

10378.72 4095.07

2.53

0.08

3.07

and boxplot analysis. Meanwhile as shown in Table 5, the t-test shows that all the t-stat values are higher than t-critical (t-stat N t-critical two tail (tα/2, df)), thereby the Ho: μ1 = μ2 is rejected. This indicates that there are significant differences between mean values of measured dose rate for metamorphic and sedimentary regions of Kuala Lumpur and other states. This further strengthened by the result of ANOVAsingle factor test (F-value of 2.534 less than F-critical of 3.074) in Table 6 which indicated that no significant difference between mean values of Silurian and Carboniferous regions for Northern states, Perak and Selangor. Apparently, this shows a good agreement with the previous results of mean comparison and boxplot analysis. Owing to natural feature of low radioactivity and background radiation in these geological regions, any change or enhancement of background dose rate in these regions can be clearly observed by statistical means.

In order to estimate the dose enhancements from TENORM impacts due to ubanisation, the average and range values of background dose rate for geology involved were estimated based on cumulative probability plot technique proposed by Sinclair (1974). The baseline data of dose rate (n = 1875) from previous study (Sanusi et al., 2016a) for western states, i.e. northern states, Perak, Selangor, Negeri Sembilan and Melaka was utilised in this analysis. Figs. 5, 6, and 7 graphically showed the analysis results. As tabulated in Table 7, the estimated values of mean (range); x ( x  s) of background dose rate for granitic, Silurian - Ordovician and Carboniferous are 221 ± 1 nGy h−1 (160–273 nGy h−1), 168 ± 2 nGy hr−1 (110–221 nGy hr−1) and 104 ± 1 nGy h−1 (78–117) nGy h−1, respectively. By subtracting these background values from the measured dose rates for all geological regions, the enhancement values of dose rate in Kuala Lumpur can be estimated. As shown in Table 7, the enhancements of dose rate in granitic, Silurian - Ordovician and Carboniferous regions were found to be 57 ± 12, 74 ± 8 and 134 ± 11 nGy h−1, respectively, with an average of 87 ± 7 nGy h−1 for the whole federal territory.

3.3. Radioactivity levels in urban soil As tabulated in Table 8, the radioactivity levels of the main primordial radionuclides 238U, 232Th and 40K in urban soil were relatively higher than in other soil types, i.e. peat, marine, metamorphic and sedimentary based soils with the concentration mean values were 95, 191 and 727 Bq kg−1. The radioactivity level of 238U and 232Th in urban soil in Kuala Lumpur were comparable with granitic soil (Lee et al., 2009) and riverine soil (Sanusi et al., 2016a), except for 40K which is 2 times higher than granitic and riverine soil. These values are higher than the average concentrations of 238U (66 Bq kg− 1), 232 Th (82 Bq kg−1) and 40K (310 Bq kg−1) in soils in Malaysia as reported by UNSCEAR (2000) based on preliminary survey of soil radioactivity conducted by Malaysian Nuclear Agency which involved about more than 700 soil samples in 214 different measurement sites throughout the country (Omar et al., 1991). To identify the major sources of measured background dose rate in Kuala Lumpur, the dose rates in air were calculated using concentrations of 238U, 232Th and 40K and conversion factors of 0.462, 0.604, 0.042 nGy h− 1 per Bq kg− 1 for 238U, 232Th and 40K, respectively (UNSCEAR, 2000). As shown in Fig. 8, most of the measured dose rate

Fig. 5. Cumulative probability graphs for determination of average value and range of background γ radiation dose rate (granitic).

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

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Fig. 6. Cumulative probability graphs for determination of average value and range of background γ radiation dose rate (Silurian).

Fig. 7. Cumulative probability graphs for determination of average value and range of background γ radiation dose rate (Carboniferous).

in Kuala Lumpur was linearly correlated with the calculated dose, with linear model of y = (0.76 ± 0.19)x + (16.93 ± 47.16). The model indicates that almost 80% of the measured dose rates in air are caused by γ emitters of 238U, 232Th and 40K in urban soils. The dashed-lines in Fig. 8 illustrated 95 % confidence intervals of mean of fitted line plot. Table 7 Result of cumulative probability plot analysis and estimation of dose rate due to TENORM Geological region

n

Background dose rate (nGy h−1)

n

TENORM contribution (nGy h−1)

Granite Silurian-Ordovician Carboniferous Mean

1127 286 462

221 ± 1 (160–273) 168 ± 2 (110–221) 104 ± 1 (78–117)

17 34 20

57 ± 12 (5–171) 74 ± 8 (3–180) 134 ± 11 (48–244) 87 ± 7 (3–244)

Parenthesis () indicates range value.

The small differences between calculated and measured dose rates can be considered due to cosmic radiations and measurement uncertainties of the instrument. To evaluate the γ response on the detector attributed by cosmic rays, some measurements were taken on the sea, away from the ground. The results obtained were found to be b10 nGy h−1. This result is compatible with the y-intercept of linear model in Fig. 8 which showed that at null reading of the detector (Dm), there is additional by 16.93 ± 47.16 nGy h−1 of dose rate indicated by Dc. Similar results were also obtained from other studies by Lee et al. (2009) (~9 nGy h−1) and Tajuddin et al. (1994) (~10 nGy h−1). It can also be assumed that there is no dose contribution from anthropogenic source of Cs137 to the total dose rate measured in Kuala Lumpur, since the radioactivity levels of Cs137 were extremely low in Peninsular Malaysia (1.2 ± 0.3 Bq kg−1), that is equivalent to b 1 nGy h−1 (Omar et al., 1991; Riduan et al., 2012).

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

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M.S.M. Sanusi et al. / Environment International xxx (2017) xxx–xxx

Table 8 Comparison of concentration of natural radionuclides for urban soil in Kuala Lumpur and other soil types in other states. Soil classification/type

n

Mean ± S.E (Bq kg−1) 238

Disturbed soil Urban soil Sedentary soil 1 Granitic soil 1 Metamorphic and sedimentary based soil 2 Metamorphic and sedimentary based soil 3 Metamorphic and sedimentary based soil Transported soil 1 Marine soil 2 Marine soil 2 Riverine soil 1 Peat 2 Peat

U

References 232

40

Th

K

16

95 ± 12

191 ± 23

727 ± 130

This study

128 18 37 7

112 ± 18 71 57 ± 6 32 ± 5

246 ± 21 101 104 ± 9 108 ± 14

277 ± 127 190 193 ± 39 491 ± 111

Lee et al., 2009 Apriantoro, 2008 Sanusi et al., 2016a Ramli et al., 2013

7 11 11 7 11

46 53 ± 11 93 ± 8 52 55

105 123 ± 13 162 ± 15 85 99

310 374 ± 121 295 ± 40 207 242

Apriantoro, 2008 Sanusi et al., 2016a Sanusi et al., 2016a Apriantoro, 2008 Sanusi et al., 2016a

1 – Perak State; 2 – Western states; 3 – Perlis and Kedah states.

3.4. Isodose map of Kuala Lumpur and effective dose received by the population The inverse distance-weighted (IDW) interpolation technique was employed for isodose mapping using mapping software ESRI ArcGIS 9.3 (Childs, 2004). The isodose map in Fig. 9 spatially showed the dose gradient of total radiation exposure from the background component and TENORM contributions due to mining and urbanisation impacts. Additionally, analysis result of boxplot in Fig. 10 is provided to statistically verify the presented spatial distribution of dose rate in Fig. 9 owing to insufficient dose measurements to support the interpolated data by IDW technique. The correlations of geological background and types of area in boxplot in Fig. 10 indicated a good agreement with the spatial distribution of dose rate. As shown in Figs. 9 and 10, most of the former tin mining areas in Kuala Lumpur show high dose rate (200–300 nGy h−1) except for Setapak - Wangsa Maju areas and minor localities in the west of Seri Petaling which indicated moderate dose rate range of 150–200 nGy h− 1. Elevated dose rate (200– 300 nGy h−1) were identified in intense urbanisation areas, i.e. Kuala Lumpur Centre, Brickfield, Bangsar, Pudu and few residential areas of Salak Selatan, Bandar Tun Razak, Cheras, Seri Petaling and Sungai Besi. High dose rate levels measured in Cheras and southern-east areas of Kuala Lumpur can be considered due to high background radiation contribution from granitic background and small contribution from TENORM. A few radiation exposure anomalies higher than 300 nGy h−1 (orange colour) were identified in the north and centre of Kuala Lumpur, southern-east Pudu (Taman Kobena), north Sentul (Tasik Metropolitan), and nearby areas in Seri Petaling (Taman Desa

Fig. 8. Plotted data of in-situ measured dose rate, Dm against calculated dose rates, Dc.

Petaling and Taman Salak Selatan). All of these localities are residential areas except for the anomalies areas in the north and centre of Kuala Lumpur which is the core areas of urbanisation. To calculate the mean of annual effective dose (AED) for baseline purpose (Jibiri, 2001), the proposed method from UNSCEAR (2000) are used;  
 −1 AED mSv y−1 ¼ mean dose rate nGy h  8760 h  0:2  0:7 Sv Gy−1

ð6Þ

Fig. 9. Isodose map of the study area based on in-situ measured dose rates.

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

M.S.M. Sanusi et al. / Environment International xxx (2017) xxx–xxx

9

3.5. Risk of stochastic effect and mortality due to lifetime radiation exposure

Fig. 10. Boxplot of dose rate based on geological background and types of area (mining, non urbanised and urbanisation area).

In order to take account of shielding factor by buildings, a factor 0.2 of outdoor occupancy was used, whilst 0.7 Sv Gy−1 is dose conversion factor (DCF) for an adult (ICRP 60, 1990; UNSCEAR, 2000). The DCF for adult was chosen to represent an average population (ICRP 74, 1996) of Kuala Lumpur, since 57% of the population in Kuala Lumpur is adult (963,891 out of 1,681,591) (EPU, 2016). The estimated AED for all districts in Kuala Lumpur are tabulated in Table 9. By assuming no variation in dose rate, each individual in Kuala Lumpur averagely received an effective dose of 0.31 ± 0.01 mSv per year due to outdoor exposures from background radiation and TENORM contribution. The highest dose area is indicated by district of Bandar Tun Razak, with mean of 0.35 ± 0.02 mSv y−1 and ranged from 0.26 to 0.48 mSv y−1. Meanwhile the lowest dose areas are indicated by district of Setiawangsa (0.27 ± 0.01 mSv y−1) and Lembah Pantai (0.27 ± 0.02 mSv y−1). In the case of radiation exposure from background and TENORM, the International Commission on Radiological Protection (ICRP) has classified it as the “existing exposure” situation (ICRP 103, 2007). In the system of radiological protection, ICRP stated that the reference level used in conjunction with the optimisation of protection to restrict individual dose due to “existing exposure” is between 1 mSv and 20 mSv y−1. The mean AED of 0.31 ± 0.01 mSv y−1 received by members of public in Kuala Lumpur is below ICRP reference range and too low to cause an acute radiation effects. Nevertheless, in terms of lifetime exposure risk, such exposures would potentially give rise to stochastic effects in members of the public (ICRP 103, 2007). Table 9 Annual effective dose (AED) received by population in Kuala Lumpur. District

Bukit Bintang Titiwangsa Setiawangsa Wangsa Maju Batu Kepong Segambut Lembah Pantai Seputeh Bandar Tun Razak Cheras All districts

n

5 6 3 3 11 3 11 5 7 13 4 71

AED mSv y−1 Mean ± S.E

Range

0.30 ± 0.04 0.33 ± 0.02 0.27 ± 0.01 0.29 ± 0.01 0.28 ± 0.02 0.29 ± 0.05 0.30 ± 0.01 0.27 ± 0.02 0.31 ± 0.03 0.35 ± 0.02 0.34 ± 0.03 0.31 ± 0.01

(0.19–0.41) (0.27–0.43) (0.25–0.29) (0.27–0.31) (0.20–0.43) (0.19–0.37) (0.26–0.32) (0.21–0.32) (0.25–0.43) (0.26–0.48) (0.29–0.43) (0.19–0.48)

The radiological protection for low-level dose, LLD (environmental sources or exposures below 100 mSv and 100 mGy of low-linear energy transfer (LET) radiation) is mainly concerned with the protection against stochastic effects i.e., cancer and heritable effects (ICRP 103, 2007). To estimate the potential radiation risks on the radiationexposed population in Kuala Lumpur, the cancer risk estimates based on BEIR VII report (Biological Effects of Ionizing Radiation) were used (BEIR VII, 2006). The BEIR VII risk estimates were chosen over ICRP sex-averaged risk estimates mainly to represent sex-specified risks among population in the study area. Nevertheless, both estimates are compatible (i.e., with slight discrepancy by 4/3) (ICRP 103, 2007) since the ICRP estimates were reduced by a DDREF of 2, which is within 95% confidence interval of BEIR VII's DDREF (1.1–2.3). In addition, the BEIR VII estimates as well as ICRP estimates were majorly derived from similar epidemiology database i.e., Japanese Life Span Study (LSS) of A-bomb survivors (ABS) from atomic bomb dosimetry system, DS02. The risk modelling involved, in total 13,000 cancer incidences and 10,000 cancer deaths from Hiroshima-Nagasaki ABS studies. Other epidemiologic data i.e., from medical radiation, occupational radiation, and environmental studies also used in their cancer risk modelling (BEIR VII, 2006; ICRP 103, 2007). For estimating lifetime attributable risk (LAR) of cancers between different populations, the BEIR VII committee have used combined risk estimates based on relative and absolute risk transport which have been adjusted by a dose and dose-rate effectiveness factor (DDREF) of 1.5, except for leukaemia, which is based on a linear-quadratic model. These estimates and their calculation examples can be found in the BEIR VII report (Table 12D1–12D3, pp. 311–312; and Annex 12D, pp. 310, respectively). Table 10 shows the results of risk values per 100,000 for a person in Kuala Lumpur being diagnosed with cancer

Table 10 Risks for a person being diagnosed with cancer incidences or dying of cancer due to lifetime γ radiation exposure based on NAS BEIR VII risk estimates.⁎ Background + TENORM exposures (high dose area, Bandar Tun Razak)

TENORM exposures (throughout Kuala Lumpur)

Exposure cases

Background + TENORM exposures (throughout Kuala Lumpur)

Cancer site

Cancer incidence

Cancer Cancer Cancer Cancer Cancer mortality incidence mortality incidence mortality

Male Stomach Colon Liver Lung Prostate Bladder Other Thyroid All solid Leukaemia All cancers

11 47 8 42 14 30 85 6 244 29 273

6 23 6 44 3 7 37 – 125 21 146

12 54 9 48 16 35 98 7 279 34 313

7 27 7 50 3 8 43 – 144 24 167

4 16 3 15 5 10 29 2 84 10 94

2 8 2 16 1 2 13 – 43 7 50

Female Stomach Colon Liver Lung Breast Uterus Ovary Bladder Other Thyroid All solid Leukaemia All cancers

14 32 4 101 98 6 13 31 94 33 426 22 448

8 15 3 90 23 2 8 9 43 – 202 17 219

16 36 4 115 112 7 15 36 107 38 488 26 513

10 17 3 103 27 2 9 11 49 – 231 19 250

5 11 2 35 34 2 4 11 32 11 147 8 155

3 5 1 31 8 1 3 3 15 – 70 6 76

⁎ Risk value per 100,000.

Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009

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M.S.M. Sanusi et al. / Environment International xxx (2017) xxx–xxx

incidences and dying of cancer due to γ radiation exposure throughout life. The risks were estimated based on different exposure cases i.e., total contribution from background and TENORM exposures throughout Kuala Lumpur and in high dose area (Bandar Tun Razak district), and single contribution from TENORM exposures throughout Kuala Lumpur. By considering an average life expectancy of 73.8 years for each individual in Kuala Lumpur (Department of Statistics Malaysia, 2010), insignificant variation of dose rate, and occupancy factor of 0.2, the risks were estimated based on mean values for each exposure case. For male the risk of being diagnosed with a solid cancer due to total contribution from background and TENORM exposures in Kuala Lumpur was estimated to be 244 per 100,000, whereas for Leukemia, 29 per 100,000 (~3 in 10,000). These yield a total risk of about 27 per 10,000 for being diagnosed with cancer. Meanwhile for female, the risk of being diagnosed with all types of cancer was estimated to be 9 in 2000. For case of high exposure area (background and TENORM) i.e., district of Bandar Tun Razak, the expected risks of cancer incidence incurred by male and female increased slightly by 1 per 2500 and 7 per 10,000. As a result of urbanisation impacts, the contributions of TENORM are expected to rise the risks of all sites-cancer by 9 per 10, 000 among male population in Kuala Lumpur, whereas for female are 1 per 625. For mortality risks in Kuala Lumpur, as tabulated in Table 10 all estimated risks for a person die due to cancer are relatively lower than the cancer incidence risks except, lung cancer for male. Overall, female is more radiosensitive than male for both cancer incidence and mortality except for colon cancer, liver cancer and leukaemia. The highest risks for both cancer incidence and mortality are indicated by female, 1 in 200 and 1 in 500, respectively (448 and 231 rounded to the nearest hundred). Although the presented estimated risks are too low, they are still considered to have potential to cause cancer incidences or even mortality owing to enhanced background radiation exposure up to almost 4 times higher than the world average of 59 nGy h− 1 (UNSCEAR, 2000). 4. Conclusion The study found that the dose levels of background γ radiation in Kuala Lumpur is technically enhanced by the contamination of 238U, 232 Th and 40K from urbanisation activities. The radioactivity contaminations are believed to be originated from former tin mining of Klang Valley and as a result of soil pollution from NORM in construction materials. The mean value of measured dose rates in 71 sampling locations in Kuala Lumpur was found to be 251 ± 6 nGy h−1 and ranged from 156 to 392 nGy h−1. The measured values are relatively 4 times higher than for the global average values (59 nGy h−1). The ANOVA test and t-test have statistically verified the enhancement of background radiation exposure in Kuala Lumpur. The analyses results have showed that the enhancements of background radiation dose rate only significant in the geological background regions of metamorphic and sedimentary. Meanwhile for granitic region, the dose enhancement are not significant. Nevertheless, in terms of tendency of dose range it can be concluded that there is significant certainty of higher dose range in granitic region of Kuala Lumpur compared to other states. Based on cumulative probability plot analyses, the mean values of dose enhancement due to TENORM in granitic, Silurian and Carboniferous regions were found to be 57 ± 12, 74 ± 8 and 134 ± 11 nGy h−1, respectively. Based on gamma spectrometric analysis of soil samples, the radionuclides of 238U, 232Th and 40K have been identified as the major sources of high radiation exposure in Kuala Lumpur. The correlation between measured and calculated dose rate based on radionuclide concentration shows that almost 80% of the measured dose rates in air are caused by γ emitters of 238U, 232Th and 40K in urban soils. Based on fitted-linear model of correlation, the discrepancy of ~20% between calculated and measured dose rate can be considered due to cosmic radiations and measurement uncertainties of the instrument.

The mean of AED received by individual in Kuala Lumpur was estimated to be 0.31 ± 0.01 mSv y−1. Meanwhile for high dose area i.e., Bandar Tun Razak district, the estimated mean of AED was found to be 0.35 ± 0.02 mSv y−1 and ranged 0.26–0.48 mSv y−1. Nevertheless, these values are lower than the recommended reference level, i.e. 1 mSv to 20 mSv y− 1 as proposed by the ICRP. The effective doses due to TENORM and background radiation exposures in the study area are too low to cause deterministic and acute radiation effects (UNSCEAR, 2000). Nevertheless, the estimated risks of cancer incidence and mortality in this study have shown that there are probabilities for a person in Kuala Lumpur being diagnosed with cancer and dying of cancer. Based on the mean value of AED, the risks of being diagnosed with all types of cancer for male and female were estimated to be 27 per 10,000 and 9 in 2000, respectively. Meanwhile, for high exposure area, the risks of being diagnosed with all types of cancer for male and female were estimated to be 3 per 1000 and 1 per 200, respectively. As a result of urbanisation impacts, the contributions of TENORM are expected to rise the risks of all sites-cancer by 9 per 10, 000 among male population in Kuala Lumpur, whereas for female are 1 per 625. For mortality risks, all estimated risks for a person die due to cancer are relatively lower than the cancer incidence risks except, lung cancer for male. Acknowledgement The authors would like to record appreciations to Universiti Teknologi Malaysia and Atomic Energy Licensing Board Malaysia (AELB) for providing various facilities and opportunities, and Ministry of Science Technology and Innovation Malaysia for sponsoring the study under consultation project (Consultation reference no: AELB/BDKS/212012), and the GTIM Sdn. Bhd. for management support. References AELB, 1991. Radiological Hazards Assessment at Mineral Processing Plants in Malaysia. Atomic Energy Licensing Board of Malaysia (LEM/LST/I6/pind. 1). Ali, K.K., 2012. Radioactivity in building materials in Iraq. Radiat. Prot. Dosim. 148 (3), 372–379. Almayahi, B.A., Tajuddin, A.A., Jaafar, M.S., 2013. Radiation hazard indices of soil and water samples in Northern Malaysian Peninsular. Appl. Radiat. Isot. 70, 2652–2660. Amrani, D., M. Tahtat, M., 2001. Natural radioactivity in Algerian building materials. Appl. Radiat. Isot. 54, 687 – 689. Ang, L.H., Ho, W.M., 2004. A demonstration project for afforestation of denuded tin tailings in Peninsular Malaysia. Cuod. Soc. Esp. Cien. For. 17, 113–118. Apriantoro, N.H., 2008. Radiological Study in Perak State and its Radiological Health Impact. (Ph.D thesis). Universiti Teknologi Malaysia, Johor Bahru, Malaysia. Bahari, I., Mohsen, N., Abdullah, P., 2007. Radioactivity and radiological risk associated with effluent sediment containing technologically enhanced naturally occurring radioactive materials in Amang (tin tailings) processing industry. J. Environ. Radioact. 95, 161–170. Bahrin, T.S., 1981. The utilization and management of land resources in Malaysia. GeoJournal 5 (6), 557–561. BEIR V.I.I., 2006. Health risks from exposure to low levels of ionizing radiation, Phase II. National Research Council. National Academy Press, Washington, DC. Carver, R.H., Nash, J.G., 2000. Doing Data Analysis With SPSS 10.0. first ed. Duxbury Publication, USA. Childs, C., 2004. Interpolating Surfaces in ArcGIS Spatial Analyst. ESRI Education Services. ArcUser (https://www.esri.com/news/arcuser/0704/files/interpolating). Chong, C.S., Ahmad, G.U., 1982. Gamma activity of some building materials in West Malaysia. Health Phys. 43 (2), 272. DAPM, 2002. Map of Soil Types in Peninsular Malaysia. Department of Agriculture, Peninsular Malaysia. Kuala Lumpur, Malaysia. DBKL, 2016. Land use and Development Strategy. Official Portal Dewan Bandaraya Kuala Lumpur (Kuala Lumpur City Hall) (http://www.dbkl.gov.my/pskl2020/english/land_ use_and_development_strategy/index.htm). Department of Statistics, Malaysia, 2010. Annual Book of Statistics Malaysia 2011. Malaysia National Printing, Bhd, Kuala Lumpur, Malaysia. DGSM, 1985. Map of Geological Features in Peninsular Malaysia. eighth ed. 1985. Department of Geological Survey Malaysia, Kuala Lumpur, Malaysia. DMM, 1980. Ex-mining Land Map in Kuala Lumpur and Adjacent. Department Mining Malaysia. Internal report – unpublished. EPU, 2016. Population by sex, Ethnic Group and age, Malaysia, 2010. Economic Planning Unit. Prime Minister’s Department Malaysia, Putrajaya, Malaysia. Hails, J.R., 1976. Placer deposits, chapter 5. Supergene and Surficial Ore Deposits. Textures and Fabrics. Volume 3 in Handbook of Strata-Bound and Stratiform Ore Deposits (ISBN: 978-0-444-41403-8).

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Please cite this article as: Sanusi, M.S.M., et al., Assessment of impact of urbanisation on background radiation exposure and human health risk estimation in Kuala Lumpur, Malaysia, Environ Int (2017), http://dx.doi.org/10.1016/j.envint.2017.01.009