Natural radioactivity level of clay , ceramic , and stone cooking dishes in Saudi Arabia

Standards and guidelines are needed in the manufacture of household cooking dishes from clay, ceramic, and stone in Saudi Arabia. The radioactivity levels due to the presence of 40 K, 232 Th, and 226 Ra in these materials were determined using gamma spectrometry equipped with high purity germanium (HPGe) detector. The activity concentrations of 226 Ra ranged from 5.75 Bq kg −1 (Yemen stone sample) to 192.35 Bq kg −1 (China ceramic sample), those of 232 Th ranged from 6.17 Bq kg −1 (Yemen stone sample) to 192.41 Bq kg −1 (China ceramic sample), and those of 40 K ranged from 43.92 Bq kg −1 (clay sample manufactured in Bahrah, Saudi Arabia) to 656.96 Bq kg −1 (ceramic sample from Romania). Radiological indices were measured for all samples to ascertain the potential radiation health hazards. The average concentrations for 226 Ra and 232 Th and the absorbed dose rate (DR) in clay and ceramic dishes exceeded the permissible global limits, with the exception of clay samples from Makkah, Saudi Arabia. The 226 Ra and 232 Th concentrations in all cooking dishes manufactured from stone were within safety limits. However, most of the average values obtained for the activity concentration of 40 K exceeded the recommended limit. The radium equivalent (Raeq), annual gonadal dose equivalent (AEDE), external hazard index (Hex), and gamma activity index (Iγ) were found to be below the internationally accepted safe limit, except in a ceramic sample imported from China. The sample also had an annual effective dose (AEDE) that slightly above unity. The concentrations of a total of 33 chemical elements were estimated by using an ARL QUANT’X energy-dispersive X-ray fluorescence spectrometer. In most samples, the elements’ concentrations exceeded the reference level values. In conclusion, care must be taken when using cooking dishes manufactured from clay, ceramic, and stone.


INTRODUCTION
Daily exposure to the natural radionuclides 232 Th, 226 Ra, and 40 K is undesirable.They cause an internal exposure risk resulting from radon and its decay products and an external exposure risk due to their gamma emission (United Nations Scientific Committee on the Effect of Atomic Radiation [UNSCEAR], 2000; Amin and Naji, 2013).Chronic exposure to low doses of natural radioactivity can cause adverse health effects (Najam et al., 2015).The most serious involve increased probability of cancer and birth defects (Faisal et al., 2014).Most household cooking dishes manufactured from clay, ceramic, and stone contain various concentrations of the natural radionuclides 226 Ra,232 Th and 40 K.The precise concentrations depend on the chemical composition of the material, which is related to the geological conditions and geophysical characteristics of their origin (Salas et al., 2006).The materials may contain radionuclides from both natural sources and waste products in addition to some minerals from certain slags.The present study centers on radiological baseline information of the Jeddah region in particular and Saudi Arabia in general.
Many ways exist for analyzing trace elements in a material, including portable energy-dispersive X-ray fluorescence (EDXRF) spectrometry with radioisotope excitation.This method is useful and significantly reduces the number of samples needed for analysis (El-Taher, 2012;Sitko et al., 2004).
The aims of the present study were to analyze household cooking dishes manufactured from clay, ceramic, and stone (1) to determine the natural radionuclide levels using high-resolution gamma-ray (HPGe) spectrometry to evaluate the radiological risks and human exposure, and (2) to specify the concentrations of elements using EDXRF spectrometry.

Sampling and sample preparation
A total of 20 samples of household cooking dishes used in Saudi Arabia were collected from local stores.Four samples were manufactured in Saudi Arabia, and the other 16 samples were imported from different foreign countries (Table 1).Each sample dish was crushed and sieved through a 1-mm mesh size to ensure homogeneity of the samples for testing.Weighted samples were placed in standard polyethylene beakers (650 cm 3 volume).The beakers were completely sealed and left for 4 to 5 weeks prior to gamma spectrometric analysis to attain secular equilibrium between radium, thorium, and their progenies products to ensure that radon gas was restricted to the beaker and the decay products remained in the sample (Hassan et al., 2010;Alharbi, 2013;Guidotti et al., 2015).For elemental analysis using EDXRF spectrometry (ARL QUANT'X EDXRF, Thermo Electron Corp., Middleton, WI), the dry samples (at room temperature) were crushed to a fine powder in an agate mortar, then sifted through a 0.25-mm sieve.The powder was then manually pressed into the sample holder, following the procedures described by Hartyàni et al. (2000).

Measurement of specific activity with gamma spectrometry
The specific activities of226 Ra, 232 Th, and 40 K in the samples were Stone Yemen measured using a gamma spectrometry system with a high-purity germanium (HPGe) coaxial detector with a relative efficiency of 25% and a full width at half maximum (FWHM) of 2.0 keV at 1332 keV of 60 Co (Darko et al., 2012;Rajeshwari et al., 2014).The system was calibrated for energy and absolute efficiency, and all measurements were conducted for 10 h.The 232 Th concentration was determined from the average concentrations of 212 Pb (238.6 keV), 212 Bi (727.25keV), 212Tl (583.1 keV), and 228 Ac (911.1 and 338.4 keV) in the samples, while the 214 Pb (351.9 and 295.09 keV) and 214 Bi (609.3, 1120.27, and1764.5 keV) decay products were used to determine the average concentrations of 226 Ra.The average concentrations of 40 K and 137 Cs were determined through 1460.3 keV and 661.66 keV energy photopeaks, respectively.The radioactivity concentration C of these radionuclides was calculated using the following formula (Beretka and Mathew, 1985): where Aa is the intensity of gamma-line in a radionuclide (counts per second), ε is the efficiency for each gamma-ray line observed for the same number of channels for the sample or the background, Pr is the absolute transition probability of the gamma-ray decay, and w is the weight in kilograms of the sample.

RESULTS AND DISCUSSION
The activity concentrations of 226 Ra, 232 Th, and 40 K in the household cooking dishes were determined by using a HPGe detector, and the results are summarized in Table 2.The highest average activity concentrations of  Cs was 3.17 Bq kg −1 from stone sample D17.Cesium 137 was not detected in four samples (Table 2): clay sample D1 imported from Egypt and stone samples D18, D19, and D20 imported from Indonesia, China, and Yemen, respectively.Table 2 shows that the concentrations of

Radium equivalent activity, Ra eq
To evaluate the potential health effects of gamma radiation associated with using cooking dishes made from clay, ceramic, and stone, the radium equivalent activity index (Ra eq ) was determined by using the following expression (Beretka and Mathew, 1985): where in ceramic samples, and 22.56-97.85Bq kg −1 in stone samples.All Ra eq values for the cooking dish samples were lower than the safety limit value of 370 Bq kg −1 , except for ceramic sample D16 from China (Ademola, 2009;Saleh and Abu Shayeb, 2014).The Ra eq values are listed in Table 3.

Absorbed dose rate, in air D R (nGy h −1 )
Calculating the gamma absorbed dose rate in air is important because it is the first step in evaluating the    ), was determined by using the specific activity concentrations (Bq kg  3. The highest D R was 224.17 nG h −1 in ceramic sample D16, which was from China, and the lowest value of D R was 10.71 nG h −1 in stone sample D20, which was from Yemen.All D R values were over the international recommended limit (57 nGy h −1 ) (UNSCEAR, 2000;Sowole, 2014), except for clay sample D7, which was manufactured in Makkah, Saudi Arabia, and all stone samples.

Annual gonadal dose equivalent (AGDE)
The annual gonadal dose equivalent (AGDE) associated with the specific activities of 226 Ra, 232 Th, and 40 K in household cooking dishes manufactured from clay, ceramic, and stone materials was calculated using the following formula (Augustine et al., 2014): The obtained AGDE values are listed in Table 3.The AGDE values varied from 0.08 to 1.54 mSv y −1 . The obtained values in all samples are higher than the world average of (300 µSv y −1 ) (UNSCEAR, 2000) except in clay sample D7 and in all stone samples.

Annual effective dose (AEDE indoor or E air )
The estimated annual effective dose equivalent received by an individual was calculated by using a conversion factor of 0.7 Sv Gy −1 , which is used to convert the absorbed rate to member effective dose equivalent with an outdoor occupancy of 20 and 80 % for indoors (UNSCEAR, 1993;Ajayi, 2009).The annual effective doses in (mSv y −1 ) were determined from the following formula (Beretka and Mathew 1985): The estimated annual effective dose rates in air are given in Table 3.None of the values obtained for the annual effective dose exceeded 1 mSv y −1 , except for sample D16.The individual effective dose limits for normal exposure in the general public is defined by the ICRP (2007).

External hazard index, H ex
To limit the external gamma radiation dose from household cooking dishes to less than 1.5 mSv y −1 , the external hazard index H ex was calculated by using the following equation (Lu et al., 2012): where  Ra ,  Th , and  K are the activity concentrations (Bq kg .The calculated values of  ex for the studied materials ranged from 0.04 to 1.36 (Table 3).The  ex values for all investigated samples, except for sample D17, were less than unity (Xhixha et al., 2013).

Activity index, I γ
To estimate the radiation hazard associated with 226   3).The values for all investigated samples were below unity, corresponding to an annual dose range of 0.3 to 1 mSv y −1 , except those for sample D16.
Fourteen samples contained Ba exceeding the concentrations reported by Kabata-Pendias and Mukherjee ( 2007), and one sample was within the reference limit.Elements Th and U were detected in samples D11, D12, D14, D16, and D20 and in samples D5, D9, D10, D13, D14, D16, and D20, respectively, but not in the remaining samples.Potassium was found in all samples, except for D8, D11, D17, and D18.The K concentrations varied between 0.86% (D12) and 6.45% (D9), and except for samples D6 and D12, they exceeded the values reported by Kabata-Pendias and Mukherjee (2007).Calcium concentrations ranged from 1.16% (stone sample D20 from Yemen) to 33.16% (ceramic sample D10 from Vietnam).All samples contained Ca, except for samples D3, D5, D9, D14, and D16, and some (D4, D6, D8, D11, D12, D13, D17, and D20) contained Ca below the mean concentration (69,600 mg/kg) calculated by Towett et al. (2013).The Mg level in the present study varied between 6.07% (60,700 mg/kg) in the clay sample D5 from Morocco and 32.18% (321,800 mg/kg) in the stone sample D17 from Jazan, Saudi Arabia.Both of these values were considerably higher than 17700 mg/kg, the mean Mg concentration reported by Towett et al. (2013).Similarly, Al was found at the highest value of 24.68% (246,800 mg/kg) for clay sample D3 imported from Spain and the lowest concentration in ceramic sample D16 with a value of 1.56% (15,600 mg/kg).Seventeen samples contained Al, all of which exceed the mean concentration of Al in soil, with the exception of D16.Sodium was detected in six samples (D4, D12, D13, D17, D18, and D20), which exceeded the mean Na concentration of 16,000 mg/kg in soil reported by Towett et al. (2013).In the current study, the Na concentration ranged from 45.69% (456,900 mg/kg) in clay sample D4 imported from Yemen to 12.97% (129,700 mg/kg) in stone sample D17 locally made in Jazan, Saudi Arabia.Zirconium (Zr), Mo, Rh, Ru, Sb, Nb, Zn and Ni were found in some samples.In comparison  , 2007), some samples in the current study had higher concentrations.In conclusion, attention must be paid to commercial marks and manufacturing country for the materials used in household cooking dishes.

Conclusion
Twenty samples of household cooking dishes in Saudi Arabia were analyzed for 33 chemical elements using ARL QUANT'X EDXRF.In addition, the natural radioactivity levels due to the presence of 40 , which was found in a stone sample manufactured in Jazan, Saudi Arabia.All values for the radionuclides measured in the investigated samples were less than the world reference limit, with the exception of the ceramic sample from China.All values for the absorbed dose rate significantly exceeded the average value, except those associated with all stone samples and with the clay sample from Makkah, Saudi Arabia.The results indicate that these materials do not pose any significant radiological risk and they are safe for use in household cooking dishes.
2008;Sahar and Naji, 2013) as shown in Figure1.The highest activity concentration of 137 and ceramic household cooking dishes exceeded world average values [(UNSCEAR], 2008;Marocchi et al., 2011;Mehra and Bala, 2014), with the exception of clay sample D7 manufactured in Makkah, Saudi Arabia.None of the stone samples exceeded the recommended limit for

Figure 1 .
Figure 1.Activity concentrations of 40 K in samples.

Figure 2 .
Figure 2. Activity concentrations of 226 Ra in samples.

Figure 3 .
Figure 3. Activity concentrations of 232 Th in samples.
, according toUNSCEAR (2008).The total dose rate D R was then calculated by the following equation(Tufail et  al.respectively, in  the samples listed in Table 2.The calculated values of D R are shown in Table the effective dose rate in air, AEDE indoor .The values of D R are given in Equation 3 for all investigated samples.
. For the safe use of household cooking dishes and a negligible radiation hazard, the values of  ex should be lower than unity and the maximum value of Ra eq must be less than 370 Bq kg −1 radioactivity level index I γ was calculated by the following equation(NEA-OECD 1979;Szabó et al. 2013):I γ = (1/300)C Ra + (1/200)C Th + (1/3000)C K (8)Where C Ra , C Th , and C K are the specific activities (in sample D7 from Makkah, Saudi Arabia, to 1.76 in ceramic sample D16 from China (Table

Table 1 .
Sample codes and countries of origin.

Table 2 .
Activity levels of 226 Ra, 232 Th, 40 K, and Raeq in household cooking dishes in Saudi Arabia.
C Ra , C Th , and C K are the activity concentrations of 226 Ra,

Table 4 .
Kabata-Pendias and Mukherjee (2007)yzed samples was higher than the range of 147 to 375 mg/kg obtained byKabata-Pendias and Mukherjee (2007)except in sample D4 and D5.The maximum and minimum amounts were observed in sample D19, with a value of 0.303% (3030 mg/kg), and sample D4, with a value of 0.020% (200 mg/kg), respectively.Titanium was detected in 14 samples, with the concentration varying from 0.236% (2360 mg/kg) in sample D18 to 3.17% (31,700 mg/kg) in sample D8.In comparison with the range 2900-15,480 mg/kg (Kabata-Pendias and Mukherjee Ra were determined using gamma spectrometry (HPGe).The concentrations of most elements exceeded the reference levels.The activity concentrations ranged between 14.52-62.71Bq kg −1 in clay samples, 34.51-170.88Bq kg −1 in ceramic samples, and 4.12-22.83Bq kg −1 in stone samples for