Food Additives & Contaminants: Part B, 2013 Vol. 6, No. 1, 55–67, http://dx.doi.org/10.1080/19393210.2012.724089
Evaluation of trace elements in selected foods and dietary intake by young children in Thailand S. Nookabkaewa, N. Rangkadilokab, C.A. Akibb, N. Tuntiwigitc, J. Saehuna and J. Satayavivadabd* a
Laboratory of Pharmacology, Chulabhorn Research Institute (CRI), Laksi, Bangkok, Thailand; bChulabhorn Graduate Institute, Bangkok, Thailand; cInter-University Program on Environmental Toxicology, Technology and Management, Asian Institute of Technology, Chulabhorn Research Institute and Mahidol University, School of Environment, Resources and Development, Klong Luang, Pathumthani, Thailand; dCenter of Excellence on Environmental Health and Toxicology, CHE, Ministry of Education, Thailand (Received 17 January 2012; final version received 21 August 2012) Elemental concentrations in rice, animal products, eggs, vegetables, fruits, infant formulas and drinking water were determined in 667 food samples randomly collected from local markets, big supermarkets and grocery stores in Bangkok, Thailand, during the period October 2005–August 2008. Samples were digested with nitric acid and analysed by inductively coupled plasma–mass spectrometry. Arsenic and cadmium levels in most foods were below the maximum levels as set by international organisations. Filtered and bottled drinking water, rice, vegetables and banana contained low concentrations of arsenic, cadmium and lead. Non-polished rice had higher magnesium, calcium, manganese, iron and selenium concentrations than polished rice. Banana was a major source for manganese and selenium. Pig kidney and liver contained high levels of arsenic and cadmium. Manganese, cadmium, lead and aluminium concentrations in soybean milk could also be of concern. With respect to food safety for children, the amounts of arsenic and cadmium ingested with poultry, pig liver or rice corresponded to high weekly or monthly intake. Keywords: elements; arsenic; cadmium; foods; dietary intake; children
Introduction Currently, increasing demand for food safety has stimulated research regarding the risk associated with consumption of food contaminated with toxic elements and pesticides. Intensive food production to supply a rapidly increasing population also requires additional nutrients applied to plants and animals. Some elements can be widely spread in the environment and be taken up and accumulated in agricultural products through the application of fertilisers or supplements (Almas and Singh 2001; Zhou et al. 2005). Some are necessary nutrients for growth and function of plants. These elements include iron, zinc, copper, chromium, manganese and selenium. On the other hand, some elements such as cadmium, arsenic, lead and mercury are toxic and can contaminate the human food chain. Application of commercial fertilisers, manures and sewage sludge containing toxic elements, pollution from mining and industry can also contaminate foodstuffs (Gimeno-Garcı´ a et al. 1996; Mazej et al. 2010; Pritchard et al. 2010). These toxic elements are not biodegradable, some having long biological halflife and they can accumulate in organs and may lead to undesirable side effects in the future.
*Corresponding author. Email: [email protected] ß 2013 Chulabhorn Research Institute
Food and drinking water are the major sources of exposure to toxic chemicals. Therefore, exposure and risk of element(s) toxicity are modulated by the diet and nutritional status. Special concern should be given to infants and young children. When growing, breast milk alone is not sufficient to meet the child’s nutritional needs. Therefore, complementary foods such as rice, meat, vegetable and infant formula are needed to fill the gap between nutritional requirement and milk supply. Some elements in complementary food such as Cu, Fe and Zn are essential micronutrients for biological functions in the human body, whereas some elements (e.g. Cd, As, Pb) can be toxic when taken in excess. Al concentration in milk was found to be higher in soy-based and casein hydrolysate formulae than breast milk and whey-based formulae (Hawkins et al. 1994). Infants may be at risk from Al toxicity when consuming infant formula containing more than 300 mg Al/L. Al toxicity causes encephalopathy, metabolic bone disease and microcytic anaemia (Sedman 1992). Cd exposure and accumulation also start at a young age. Its accumulation in kidney is responsible for nephrotoxicity and osteoporosis, which are observed at the adult age. In school-age children,
56
S. Nookabkaew et al.
high urinary Cd levels were associated with immunesuppressive effects (Schoeters et al. 2006). For 4– 9-year-old children, cereals like bread, pasta and rice showed the highest contribution to Cd, Hg and Pb intake (Llobet et al. 2003). Exposure to As from drinking water was associated with reduced intellectual function in 6-year-old children in Bangladesh (Wasserman et al. 2007). In addition, children exposed to either high As or fluoride in drinking water also had increased risk of reduced Intelligence Quotient scores (Rocha-Amador et al. 2007). Recently, children in India aged 13–18 years were found to have a relative higher potential risk of skin lesions caused by As-contaminated cooked rice than 1–6-year-old children (Liao et al. 2010). In Bangladesh, 10-year-old children consuming tube-well water with an average concentration of 793 mg Mn/L may be at risk from Mn-induced neurotoxicity (Wasserman et al. 2006; Bouchard et al. 2011). Researchers found a dose– response association between Mn concentrations in water and test scores of performance and verbal ability in children. Soy or rice beverages containing higher levels of Mn than milk-based infant formulas should not be used to feed infants because they may increase the risk of adverse neurological effects (Cockell et al. 2004). Intake of a wide variety of foods will help children to meet their nutrient requirements for growth. World Health Organization (WHO 2005) suggests different kinds of foods such as egg, meat (or liver), poultry, fish, rice, wheat, potato, spinach, pumpkin and guava for feeding non-breastfed children of 6–24 months of age in South Asia. Several studies in different countries have evaluated both macro elements (Ca, Mg, Na, K, P) and trace elements (Fe, Zn, Cu, Se) including some toxic elements (Pb and Cd) in various foods such as cereals, vegetables, fruit, milk and dairy products, meat and meat products and fish (Iyengar et al. 2002; Lombardi-Boccia et al. 2003; Radwan and Salama 2006). Llobet et al. (2003) reported concentrations of As, Cd, Hg and Pb in common foods (e.g. vegetables, cereals, fruits, fish and shellfish, meat, eggs) from seven cities of Catalonia, Spain, and estimated the daily intake by children, adolescents, adults and seniors. Their results showed that cereal was the group showing the highest contribution to daily intake of Cd, Hg and Pb while fish and shellfish were the main foods responsible for high As intake in children aged 4–9 years. Therefore, it is very important to study the contents of trace elements including some toxic elements (Cd, As, Pb) in various foodstuffs normally eaten by infant and young school children. The objective of this study was to determine the elemental concentrations (Mg, Ca, Mn, Fe, Cu, Zn, V, Cr, Co, Ni, Se, Mo, Al, As, Cd and Pb) in selected complementary foods usually consumed by children in Thailand. The estimation of daily intake of some
toxic elements was also calculated for children aged 6–24 months. Related regulatory agencies and parents should be concerned to minimise the intake of food and drinking water contaminated with these toxic elements in young children.
Materials and methods Reagents and apparatus Standard stock solutions of Mg, Ca, Mn, Fe, Cu, Zn, V, Cr, Co, Ni, Se, Mo, Al, As, Cd and Pb (1000 mg/L) (Fisher Scientific UK Limited, Leicestershire, UK) were used for calibration. Nitric acid 65% (w/v) (Suprapur; Merck, Darmstadt, Germany) and deionised water with a maximum conductance of 18.2 M cm1 (Milli-Q Millipore system, Bedford, MA, USA) were used for sample preparation. A microwave laboratory system (HP-500 MAR5, CEM Corporation, Mathews, NC, USA) was used for sample digestion. A hot-air oven (Memmert, Schwabach, Germany) and freeze-dryer (Labconco, Kansas City, MO, USA) were used to dry the samples. A commercial laboratory blender model HGBTWT (Waring Commercial, Torrington, CT, USA) was used for grinding the samples. Measurements of all elements were performed with an inductively coupled plasma–mass spectrometer (ICPMS; Agilent Technologies 7500c, Palo Alto, CA, USA), equipped with an integrated autosampler, G3160A, and a Babington nebuliser.
Sample collection A total of 667 food samples were randomly collected from local markets, big supermarkets and grocery stores in Bangkok, Thailand, during the period October 2005–August 2008. Samples included local and imported powder infant formulas, soybean milk, drinking water, bottled water, vegetables, banana, rice (polished and non-polished), meat and animal products and boiled chicken eggs.
Sample preparation Except infant formula and banana, all samples were washed with tap water to remove dust and rinsed twice with deionised water. Vegetable samples were studied for the edible part. Kale was divided into leaf and stem. All vegetables were dried in a heated oven until constant weight. Three bananas were peeled, then separated into the outer and inner part (approximately 0.5 cm from the surface). All banana, meat and its products and soybean milk samples were freeze-dried (maximum volume for one freeze-dried flask was 210 mL). Then dried samples were powdered with a stainless steel mixer or mortar. The pulverised and powdered samples were kept at 20 C until digestion.
Food Additives & Contaminants: Part B Eggs were boiled in water and then separated into yolk and albumin before digestion.
Sample digestion Portions (0.25 g) of the dried powders or water samples (45 mL) were transferred into polytetrafluoroethylene (PTFE) vessels. Then 6 mL of concentrated nitric acid (65%) and 2 mL of H2O (only 5 mL of HNO3 for water samples) were added into the vessels. The vessels were closed, placed on the rotating turntable of the microwave oven and the digestion process was started. The digestion was allowed to 180 psi and 190 C over 30 min and maintained at this condition for 30 min. The digested solutions were diluted to 50 mL with deionised water.
ICP-MS analysis Elemental content was determined in the clear solutions using ICP-MS. Working standard solutions were prepared each day by dilution from stock standard solutions in enough Suprapur nitric acid to give a final acid concentration similar to the digested samples. Rhodium (Rh) and germanium (Ge) were used as internal standards. The excitation power of the plasma was 1500 W; the gas flow rates for plasma gas, carrier gas and make up gas were 15.0, 0.9 and 0.3 L/min, respectively. Hydrogen and helium gases were used as reaction gases at flow rates of 4.5 and 5.0 mL/min, respectively.
Quality control Accuracy and precision were tested with five standard reference materials (SRMs); SRM 1515 apple leaves, SRM 1573a tomato leaves, SRM 1568a rice flour (US Department of Commerce National Institute Standards and Technology; NIST, Gaithersburg, MD, USA), DORM2 dogfish muscle (National Research Council, Canada) and TM-27.2 water (National Water Research Institute, Canada).
57
For some essential elements, trueness percentages of Mn, Fe, Cu and Zn were 94%–106%, 90%–106%, 89%–102% and 94%–129%, respectively. Results from ICP-MS analysis were in good agreement with certified values. Thus, it could be concluded that digestion and analysis were in accordance with quality requirements.
Drinking water Surface and ground water are the sources for drinking water in Thailand. Tap water is recommended by the Metropolitan Waterworks Authority (MWA) as being safe, especially in the Bangkok area. Moreover, filtered and bottled water are also popular. Therefore, these three types of drinking water were selected for this study. Mean values and ranges of elemental concentrations in all drinking waters are summarised in Table 2. The results were compared with the Maximum Acceptable Concentration or Maximum Allowable Concentration of drinking water quality standards of Thailand and the WHO. All elemental concentrations of filtered (n ¼ 30) and bottled drinking water (n ¼ 29) were below these limits, except 3 out of 17 brands of bottled drinking water, which contained 10–12 mg As/ L, whereas the WHO limit is 10 mg/L. This is most likely caused by the raw water used for drinking water production or the purification process. It should be noted that As and Cr were found to be higher in bottled water than tap and filtered water. Mean concentrations of Mn, Fe, Cu, Zn, Al and Pb in tap water were higher than filtered water followed by bottled water. These elements may be accumulated in the water pipeline and released into drinking water during transportation of tap and filtered water. Recent research from Deveau (2010) showed that Canadian drinking water might be a significant source of some essential elements especially Cu as this water was estimated to provide 23%–66% of daily Cu requirement. In addition, this water could provide sufficient amounts of Cr and Mn to bottle-fed infants.
Cooked egg and raw rice Results and discussion Quality control For quality control, the five SRMs listed above – SRM1515 apple leaves, SRM 1573a tomato leaves, SRM1568a rice flour, DORM2 dogfish muscle and TM-27.2 water—were used. Determination of trueness percentages, based on SRMs, ranged from 80% to 129% except trueness of As in SRM1573a (141%) and Se in TM27.2 (142%) (Table 1). The trueness percentages of total As, Cd and Pb ranged 98%–109% (except SRM1573a), 91%–104% and 80%–93%, respectively.
Table 3 shows that boiled chicken eggs contained higher concentrations of Ca, Mn, Fe, Co, Cu, Zn, Se and Mo in yolk than albumin whereas other elements did not differ. Therefore, egg yolk is a good source for essential elements, especially Ca, Fe, Zn and Se. These results agree with previous results from Uluozlu et al. (2009), who reported higher levels of Fe, Zn, Cu and Se in chicken egg yolk than in albumin. Cu concentration in chicken egg in this study was also similar to that found in duck egg (0.83 mg/g in albumin and 1.36 mg/g in yolk) from 65 farms in Taiwan, reported by Jeng and Yang (1995). However, Pb and Cd concentrations
2710 80 15,260 150 54 3 83 5 5.64 0.24 12.5 0.3 0.26 0.03 0.3a 0.09a 0.91 0.12 0.05 0.009 0.094 0.013 0.038 0.007 0.013 0.002 0.47 0.024 286 9
Certified
b
Notes: aInformation value. Background concentrations.
Mg Ca Mn Fe Cu Zn V Cr Co Ni Se Mo As Cd Pb Al
Element
3008 181 – 57.2 2.2 88.4 5.6 6.07 0.34 13.0 0.6 0.24 0.02 0.38 0.05 0.096 0.009 1.03 0.14 0.043 0.010 0.099 0.014 – 0.013 0.001 0.403 0.045 319 25
Found
SRM1515 (mg/kg) Found 11,614 1150 50,460 3430 256 20 383 37 4.81 0.45 31.1 2.7 0.838 0.080 2.03 0.21 0.584 0.048 1.59 0.17 0.064 0.013 0.446 0.034 0.158 0.026 1.43 0.10 0.538 0.05 536 63
Certified 12,000a 50,500 900 246 8 368 7 4.7 0.14 30.9 0.7 0.835 0.010 1.99 0.06 0.57 0.02 1.59 0.07 0.054 0.003 0.46a 0.112 0.004 1.52 0.04 – 598 12
SRM1573a (mg/kg)
560 20 118 6 20.0 1.6 7.4 0.9 2.4 0.3 19.4 0.5 0.007a – 0.018a – 0.38 0.04 1.46 0.08 0.29 0.03 0.022 0.002
Evaluation of trace elements in selected foods and dietary intake by young children in Thailand S. Nookabkaewa, N. Rangkadilokab, C.A. Akibb, N. Tuntiwigitc, J. Saehuna and J. Satayavivadabd* a
Laboratory of Pharmacology, Chulabhorn Research Institute (CRI), Laksi, Bangkok, Thailand; bChulabhorn Graduate Institute, Bangkok, Thailand; cInter-University Program on Environmental Toxicology, Technology and Management, Asian Institute of Technology, Chulabhorn Research Institute and Mahidol University, School of Environment, Resources and Development, Klong Luang, Pathumthani, Thailand; dCenter of Excellence on Environmental Health and Toxicology, CHE, Ministry of Education, Thailand (Received 17 January 2012; final version received 21 August 2012) Elemental concentrations in rice, animal products, eggs, vegetables, fruits, infant formulas and drinking water were determined in 667 food samples randomly collected from local markets, big supermarkets and grocery stores in Bangkok, Thailand, during the period October 2005–August 2008. Samples were digested with nitric acid and analysed by inductively coupled plasma–mass spectrometry. Arsenic and cadmium levels in most foods were below the maximum levels as set by international organisations. Filtered and bottled drinking water, rice, vegetables and banana contained low concentrations of arsenic, cadmium and lead. Non-polished rice had higher magnesium, calcium, manganese, iron and selenium concentrations than polished rice. Banana was a major source for manganese and selenium. Pig kidney and liver contained high levels of arsenic and cadmium. Manganese, cadmium, lead and aluminium concentrations in soybean milk could also be of concern. With respect to food safety for children, the amounts of arsenic and cadmium ingested with poultry, pig liver or rice corresponded to high weekly or monthly intake. Keywords: elements; arsenic; cadmium; foods; dietary intake; children
Introduction Currently, increasing demand for food safety has stimulated research regarding the risk associated with consumption of food contaminated with toxic elements and pesticides. Intensive food production to supply a rapidly increasing population also requires additional nutrients applied to plants and animals. Some elements can be widely spread in the environment and be taken up and accumulated in agricultural products through the application of fertilisers or supplements (Almas and Singh 2001; Zhou et al. 2005). Some are necessary nutrients for growth and function of plants. These elements include iron, zinc, copper, chromium, manganese and selenium. On the other hand, some elements such as cadmium, arsenic, lead and mercury are toxic and can contaminate the human food chain. Application of commercial fertilisers, manures and sewage sludge containing toxic elements, pollution from mining and industry can also contaminate foodstuffs (Gimeno-Garcı´ a et al. 1996; Mazej et al. 2010; Pritchard et al. 2010). These toxic elements are not biodegradable, some having long biological halflife and they can accumulate in organs and may lead to undesirable side effects in the future.
*Corresponding author. Email: [email protected] ß 2013 Chulabhorn Research Institute
Food and drinking water are the major sources of exposure to toxic chemicals. Therefore, exposure and risk of element(s) toxicity are modulated by the diet and nutritional status. Special concern should be given to infants and young children. When growing, breast milk alone is not sufficient to meet the child’s nutritional needs. Therefore, complementary foods such as rice, meat, vegetable and infant formula are needed to fill the gap between nutritional requirement and milk supply. Some elements in complementary food such as Cu, Fe and Zn are essential micronutrients for biological functions in the human body, whereas some elements (e.g. Cd, As, Pb) can be toxic when taken in excess. Al concentration in milk was found to be higher in soy-based and casein hydrolysate formulae than breast milk and whey-based formulae (Hawkins et al. 1994). Infants may be at risk from Al toxicity when consuming infant formula containing more than 300 mg Al/L. Al toxicity causes encephalopathy, metabolic bone disease and microcytic anaemia (Sedman 1992). Cd exposure and accumulation also start at a young age. Its accumulation in kidney is responsible for nephrotoxicity and osteoporosis, which are observed at the adult age. In school-age children,
56
S. Nookabkaew et al.
high urinary Cd levels were associated with immunesuppressive effects (Schoeters et al. 2006). For 4– 9-year-old children, cereals like bread, pasta and rice showed the highest contribution to Cd, Hg and Pb intake (Llobet et al. 2003). Exposure to As from drinking water was associated with reduced intellectual function in 6-year-old children in Bangladesh (Wasserman et al. 2007). In addition, children exposed to either high As or fluoride in drinking water also had increased risk of reduced Intelligence Quotient scores (Rocha-Amador et al. 2007). Recently, children in India aged 13–18 years were found to have a relative higher potential risk of skin lesions caused by As-contaminated cooked rice than 1–6-year-old children (Liao et al. 2010). In Bangladesh, 10-year-old children consuming tube-well water with an average concentration of 793 mg Mn/L may be at risk from Mn-induced neurotoxicity (Wasserman et al. 2006; Bouchard et al. 2011). Researchers found a dose– response association between Mn concentrations in water and test scores of performance and verbal ability in children. Soy or rice beverages containing higher levels of Mn than milk-based infant formulas should not be used to feed infants because they may increase the risk of adverse neurological effects (Cockell et al. 2004). Intake of a wide variety of foods will help children to meet their nutrient requirements for growth. World Health Organization (WHO 2005) suggests different kinds of foods such as egg, meat (or liver), poultry, fish, rice, wheat, potato, spinach, pumpkin and guava for feeding non-breastfed children of 6–24 months of age in South Asia. Several studies in different countries have evaluated both macro elements (Ca, Mg, Na, K, P) and trace elements (Fe, Zn, Cu, Se) including some toxic elements (Pb and Cd) in various foods such as cereals, vegetables, fruit, milk and dairy products, meat and meat products and fish (Iyengar et al. 2002; Lombardi-Boccia et al. 2003; Radwan and Salama 2006). Llobet et al. (2003) reported concentrations of As, Cd, Hg and Pb in common foods (e.g. vegetables, cereals, fruits, fish and shellfish, meat, eggs) from seven cities of Catalonia, Spain, and estimated the daily intake by children, adolescents, adults and seniors. Their results showed that cereal was the group showing the highest contribution to daily intake of Cd, Hg and Pb while fish and shellfish were the main foods responsible for high As intake in children aged 4–9 years. Therefore, it is very important to study the contents of trace elements including some toxic elements (Cd, As, Pb) in various foodstuffs normally eaten by infant and young school children. The objective of this study was to determine the elemental concentrations (Mg, Ca, Mn, Fe, Cu, Zn, V, Cr, Co, Ni, Se, Mo, Al, As, Cd and Pb) in selected complementary foods usually consumed by children in Thailand. The estimation of daily intake of some
toxic elements was also calculated for children aged 6–24 months. Related regulatory agencies and parents should be concerned to minimise the intake of food and drinking water contaminated with these toxic elements in young children.
Materials and methods Reagents and apparatus Standard stock solutions of Mg, Ca, Mn, Fe, Cu, Zn, V, Cr, Co, Ni, Se, Mo, Al, As, Cd and Pb (1000 mg/L) (Fisher Scientific UK Limited, Leicestershire, UK) were used for calibration. Nitric acid 65% (w/v) (Suprapur; Merck, Darmstadt, Germany) and deionised water with a maximum conductance of 18.2 M cm1 (Milli-Q Millipore system, Bedford, MA, USA) were used for sample preparation. A microwave laboratory system (HP-500 MAR5, CEM Corporation, Mathews, NC, USA) was used for sample digestion. A hot-air oven (Memmert, Schwabach, Germany) and freeze-dryer (Labconco, Kansas City, MO, USA) were used to dry the samples. A commercial laboratory blender model HGBTWT (Waring Commercial, Torrington, CT, USA) was used for grinding the samples. Measurements of all elements were performed with an inductively coupled plasma–mass spectrometer (ICPMS; Agilent Technologies 7500c, Palo Alto, CA, USA), equipped with an integrated autosampler, G3160A, and a Babington nebuliser.
Sample collection A total of 667 food samples were randomly collected from local markets, big supermarkets and grocery stores in Bangkok, Thailand, during the period October 2005–August 2008. Samples included local and imported powder infant formulas, soybean milk, drinking water, bottled water, vegetables, banana, rice (polished and non-polished), meat and animal products and boiled chicken eggs.
Sample preparation Except infant formula and banana, all samples were washed with tap water to remove dust and rinsed twice with deionised water. Vegetable samples were studied for the edible part. Kale was divided into leaf and stem. All vegetables were dried in a heated oven until constant weight. Three bananas were peeled, then separated into the outer and inner part (approximately 0.5 cm from the surface). All banana, meat and its products and soybean milk samples were freeze-dried (maximum volume for one freeze-dried flask was 210 mL). Then dried samples were powdered with a stainless steel mixer or mortar. The pulverised and powdered samples were kept at 20 C until digestion.
Food Additives & Contaminants: Part B Eggs were boiled in water and then separated into yolk and albumin before digestion.
Sample digestion Portions (0.25 g) of the dried powders or water samples (45 mL) were transferred into polytetrafluoroethylene (PTFE) vessels. Then 6 mL of concentrated nitric acid (65%) and 2 mL of H2O (only 5 mL of HNO3 for water samples) were added into the vessels. The vessels were closed, placed on the rotating turntable of the microwave oven and the digestion process was started. The digestion was allowed to 180 psi and 190 C over 30 min and maintained at this condition for 30 min. The digested solutions were diluted to 50 mL with deionised water.
ICP-MS analysis Elemental content was determined in the clear solutions using ICP-MS. Working standard solutions were prepared each day by dilution from stock standard solutions in enough Suprapur nitric acid to give a final acid concentration similar to the digested samples. Rhodium (Rh) and germanium (Ge) were used as internal standards. The excitation power of the plasma was 1500 W; the gas flow rates for plasma gas, carrier gas and make up gas were 15.0, 0.9 and 0.3 L/min, respectively. Hydrogen and helium gases were used as reaction gases at flow rates of 4.5 and 5.0 mL/min, respectively.
Quality control Accuracy and precision were tested with five standard reference materials (SRMs); SRM 1515 apple leaves, SRM 1573a tomato leaves, SRM 1568a rice flour (US Department of Commerce National Institute Standards and Technology; NIST, Gaithersburg, MD, USA), DORM2 dogfish muscle (National Research Council, Canada) and TM-27.2 water (National Water Research Institute, Canada).
57
For some essential elements, trueness percentages of Mn, Fe, Cu and Zn were 94%–106%, 90%–106%, 89%–102% and 94%–129%, respectively. Results from ICP-MS analysis were in good agreement with certified values. Thus, it could be concluded that digestion and analysis were in accordance with quality requirements.
Drinking water Surface and ground water are the sources for drinking water in Thailand. Tap water is recommended by the Metropolitan Waterworks Authority (MWA) as being safe, especially in the Bangkok area. Moreover, filtered and bottled water are also popular. Therefore, these three types of drinking water were selected for this study. Mean values and ranges of elemental concentrations in all drinking waters are summarised in Table 2. The results were compared with the Maximum Acceptable Concentration or Maximum Allowable Concentration of drinking water quality standards of Thailand and the WHO. All elemental concentrations of filtered (n ¼ 30) and bottled drinking water (n ¼ 29) were below these limits, except 3 out of 17 brands of bottled drinking water, which contained 10–12 mg As/ L, whereas the WHO limit is 10 mg/L. This is most likely caused by the raw water used for drinking water production or the purification process. It should be noted that As and Cr were found to be higher in bottled water than tap and filtered water. Mean concentrations of Mn, Fe, Cu, Zn, Al and Pb in tap water were higher than filtered water followed by bottled water. These elements may be accumulated in the water pipeline and released into drinking water during transportation of tap and filtered water. Recent research from Deveau (2010) showed that Canadian drinking water might be a significant source of some essential elements especially Cu as this water was estimated to provide 23%–66% of daily Cu requirement. In addition, this water could provide sufficient amounts of Cr and Mn to bottle-fed infants.
Cooked egg and raw rice Results and discussion Quality control For quality control, the five SRMs listed above – SRM1515 apple leaves, SRM 1573a tomato leaves, SRM1568a rice flour, DORM2 dogfish muscle and TM-27.2 water—were used. Determination of trueness percentages, based on SRMs, ranged from 80% to 129% except trueness of As in SRM1573a (141%) and Se in TM27.2 (142%) (Table 1). The trueness percentages of total As, Cd and Pb ranged 98%–109% (except SRM1573a), 91%–104% and 80%–93%, respectively.
Table 3 shows that boiled chicken eggs contained higher concentrations of Ca, Mn, Fe, Co, Cu, Zn, Se and Mo in yolk than albumin whereas other elements did not differ. Therefore, egg yolk is a good source for essential elements, especially Ca, Fe, Zn and Se. These results agree with previous results from Uluozlu et al. (2009), who reported higher levels of Fe, Zn, Cu and Se in chicken egg yolk than in albumin. Cu concentration in chicken egg in this study was also similar to that found in duck egg (0.83 mg/g in albumin and 1.36 mg/g in yolk) from 65 farms in Taiwan, reported by Jeng and Yang (1995). However, Pb and Cd concentrations
2710 80 15,260 150 54 3 83 5 5.64 0.24 12.5 0.3 0.26 0.03 0.3a 0.09a 0.91 0.12 0.05 0.009 0.094 0.013 0.038 0.007 0.013 0.002 0.47 0.024 286 9
Certified
b
Notes: aInformation value. Background concentrations.
Mg Ca Mn Fe Cu Zn V Cr Co Ni Se Mo As Cd Pb Al
Element
3008 181 – 57.2 2.2 88.4 5.6 6.07 0.34 13.0 0.6 0.24 0.02 0.38 0.05 0.096 0.009 1.03 0.14 0.043 0.010 0.099 0.014 – 0.013 0.001 0.403 0.045 319 25
Found
SRM1515 (mg/kg) Found 11,614 1150 50,460 3430 256 20 383 37 4.81 0.45 31.1 2.7 0.838 0.080 2.03 0.21 0.584 0.048 1.59 0.17 0.064 0.013 0.446 0.034 0.158 0.026 1.43 0.10 0.538 0.05 536 63
Certified 12,000a 50,500 900 246 8 368 7 4.7 0.14 30.9 0.7 0.835 0.010 1.99 0.06 0.57 0.02 1.59 0.07 0.054 0.003 0.46a 0.112 0.004 1.52 0.04 – 598 12
SRM1573a (mg/kg)
560 20 118 6 20.0 1.6 7.4 0.9 2.4 0.3 19.4 0.5 0.007a – 0.018a – 0.38 0.04 1.46 0.08 0.29 0.03 0.022 0.002
