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Food Additives & Contaminants: Part A Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tfac20
Total and inorganic arsenic in foods of the first Hong Kong total diet study a
a
a
Stephen Wai-cheung Chung , Chi-ho Lam & Benny Tsz-pun Chan a
Food Research Laboratory, Food and Environmental Hygiene Department, Centre for Food Safety, Hong Kong, China Accepted author version posted online: 19 Dec 2013.Published online: 24 Feb 2014.
To cite this article: Stephen Wai-cheung Chung, Chi-ho Lam & Benny Tsz-pun Chan (2014) Total and inorganic arsenic in foods of the first Hong Kong total diet study, Food Additives & Contaminants: Part A, 31:4, 650-657, DOI: 10.1080/19440049.2013.877162 To link to this article: http://dx.doi.org/10.1080/19440049.2013.877162
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Food Additives & Contaminants: Part A, 2014 Vol. 31, No. 4, 650–657, http://dx.doi.org/10.1080/19440049.2013.877162
Total and inorganic arsenic in foods of the first Hong Kong total diet study Stephen Wai-cheung Chung*, Chi-ho Lam and Benny Tsz-pun Chan Food Research Laboratory, Food and Environmental Hygiene Department, Centre for Food Safety, Hong Kong, China
Downloaded by [Uppsala universitetsbibliotek] at 09:26 14 October 2014
(Received 17 September 2013; accepted 12 December 2013) Arsenic (As) is a metalloid that occurs in different inorganic and organic forms, which are found in the environment from both natural occurrence and anthropogenic activity. The inorganic forms of As (iAs) are more toxic as compared with the organic As, but so far most of the occurrence data in food collected in the framework of official food control are still reported as total As without differentiating the various As species. In this paper, total As and iAs contents of 600 total diet study (TDS) samples, subdivided into 15 different food groups, were quantified by high-resolution inductively coupled plasma mass spectrometry (HR-ICP/MS) and hydride generation (HG) ICP/MS respectively. The method detection limits for both total As and iAs were 3 μg As kg−1. As the samples were prepared for TDS, food items were purchased directly from the market or prepared as for normal consumption, i.e. table ready, in the manner most representative of and consistent with cultural habits in Hong Kong as far as practicable. The highest total As and iAs content were found in ‘fish, seafood and their products’ and ‘vegetables and their products’ respectively. Besides, this paper also presents the ratios of iAs and total As content in different ready-to-eat food items. The highest ratio of iAs to total As was found in ‘vegetables and their products’. It is likely that iAs in vegetables maintained its status even after cooking. Keywords: total arsenic; inorganic arsenic; total diet study; ready-to-eat food items
Introduction Arsenic (As) is a metalloid that occurs in inorganic and organic forms and is found in the environment from both natural sources and human activities (Eisler 2000; JECFA 2011). Inorganic arsenic (iAs), including trivalent and pentavalent As, is the more toxic form of As; it may cause cancers of the urinary bladder, lung and skin, skin lesions, cardiovascular disease, neurotoxicity and diabetes (EFSA 2009; IARC 2009; JECFA 2011). Even though the toxicity of trivalent As is the highest amongst all the possible chemical species of this element, JECFA only determined the iAs benchmark dose lower confidence limit for a 0.5% increased incidence of lung cancer in humans (BMDL0.5) as 3.0 μg kg–1 body weight (bw) day–1 (in the region of 2–7 μg kg–1 bw day–1) in 2010. Therefore, there is no need to distinguish the trivalent and pentavalent As for dietary exposure studies. Intake of low levels of iAs may be unavoidable due to its ubiquitous nature and food is also recognised as the major source of iAs exposure (WHO 2003; EFSA 2009; JECFA 2011). Foods and beverages usually contain iAs at levels not exceeding 100 μg kg–1 with mean values generally less than 30 μg kg–1. However, seaweed, rice, and some fish and seafood commodities, as well as food crops grown in As-contaminated soils, may have higher iAs levels and their proportions of iAs to the total As also vary a lot (Codex 2011; JECFA 2011). *Corresponding author. Email: [email protected] © 2014 Taylor & Francis
In the Scientific Opinion from EFSA on As in food, approximately 98% of the submitted results from 15 European countries were reported as total As, and only a few investigations differentiated between the various As species. Besides, the EFSA Panel on Contaminants in the Food Chain was not able to assess the typical ratios between inorganic and organic As in different groups of foodstuffs as representative speciation data were scarce. Thus, the proportion of iAs was assumed to vary from 50% to 100% of the total As reported in food commodities other than fish and seafood, with 70% considered as best reflecting an overall average. In fish and seafood the relative proportion of iAs is small and tends to decrease as the total As content increases, and the ratio may vary depending on the seafood type. Moreover, iAs content may vary after the cooking process (Diaz et al. 2004; Devesa et al. 2008). The total diet study (TDS) has been recognised internationally as the most cost-effective way to estimate the dietary exposures to food chemicals for various population groups and to assess their associated health risks, and it provides a scientific basis for assessing food safety risks and regulating food supply (WHO 2005). In 2010, the Centre for Food Safety (CFS) started to conduct the first Hong Kong TDS, aiming to estimate dietary exposures of the Hong Kong population and various population subgroups to a range of substances, including contaminants and nutrients, and thus assess any associated health risk.
Food Additives & Contaminants: Part A In view of the differences of associated health risk between iAs and total As and limited speciation data, this paper aims to present the results of both iAs and total As contents in 150 TDS food items.
Materials and methods
Downloaded by [Uppsala universitetsbibliotek] at 09:26 14 October 2014
Food selection and sampling The latest and most comprehensive food consumption data from the Hong Kong Population-based Food Consumption Survey (FCS) were used. The FCS was conducted by CFS in 2005–07 among 5008 Hong Kong adults aged between 20 and 84 years by means of two non-consecutive 24-h dietary intake questionnaires supplemented by a food-frequency questionnaire. It revealed that over 1400 food items were consumed by the Hong Kong population (FEHD 2010). A total of 150 TDS food items were selected for the study, based on the food consumption data captured from the FCS, representing 88% of the daily ration of the average individual. Food sampling was conducted on four occasions over 1 year from March 2010 to February 2011. On each occasion three samples of each TDS food item were purchased from various retail outlets in different regions of the territory, namely Kowloon, Hong Kong Island and New Territories, and prepared as for normal consumption, i.e. table ready, in a manner most representative of and consistent with cultural habits in Hong Kong as far as practicable. Samples were brought on the same day of collection and kept for not more than 1 day in the refrigerator until sample preparation. A total of 1800 samples were collected.
Sample preparation Samples were prepared according to the standard procedures. They were then homogenised individually and combined into a composite sample. A total of 1800 samples were collected and combined into 600 composite samples. Distilled water was used for food preparation, and no salt and cooking oil were added during food preparation (FEHD 2012). Samples prepared were kept at −18°C and transferred to the laboratory for analysis as soon as possible (normally less than 3 h). The equipment used for preparing and homogenising the composite samples was thoroughly washed between each preparation (e.g. cleaning with a laboratory-grade detergent, rinsing thoroughly with hot tap water and rinsing thoroughly with deionised water) to avoid the risk of cross-contamination.
Analytical determination of total As Total As was extracted by microwave-assisted concentrated nitric acid digestion of the sample, followed by high-resolution inductively coupled plasma mass
651
spectrometry (HR-ICP/MS) determination. In brief, the composite samples (2 g) were digested in 10 ml concentrated nitric acid using Teflon high-pressure closed vessels and microwave heating for 40 min. The digestion was carried out with a four-step programme ramping from 200 psi/75°C to 500 psi/180°C at a constant power of 1200 W. The digest was diluted to 50 ml with water. The sample solution was filtered and spiked with internal standard before instrument analysis. The analytical quantification of total As was achieved by HR-ICP/MS (Thermo Element 2, Bremen, Germany), equipped with concentric nebuliser, quartz double-pass spray chamber (cooled to 2°C), and platinum skimmer and sample cone. Power was set at 1255 W. The peristaltic pump speed and sample take-up speed were set at 10 rpm and 0.5 ml min–1, respectively. Cool gas, auxiliary gas and sample gas were set at 16, 1 and 1 L min–1 respectively. Resolution was set as high, which means the resolution of 115In was at least 10 000. 75As was monitored for quantitation; 72Ge was used as the internal standard (IS). The calibration curve was established by 11 concentration levels range of 0 to 100 μg l–1 (with an IS concentration of 5 μg l–1), which a working range of LOD–2500 μg kg–1. LODs and LOQs were 3 and 15 μg kg–1 in food, and 0.6 and 3 μg kg–1 in drinking water and bottled water, respectively. For quality control, a number of CRMs were used and included typical diet (NIST SRM1548a), oyster tissue (NIST SRM1566b), rice flour (NIST SRM1568a), spinach leaf (NIST SRM1570a), bovine liver (NIST SRM1577c) and lobster hepatopancreas (NRC TORT-2). All CRMs were used as provided without further grinding. CRMs were stored under the same conditions and digested with the same protocol as the analysed food samples. The average recovery percentages of CRMs range of 97% to 123% with %RSD < 7.5%. The average spiking recovery percentage for ongoing performance monitoring was 103% (< 5% RSD). Analytical determination of iAs iAs refers to the sum of arsenite (As(III)) and arsenate (As (V)). The composite samples (2.5 g) were solubilised in around 3 ml deionised water and 18.4 ml concentrated hydrochloric acid. After reduction with 2 ml of hydrogen bromide and 1 ml of 15 mg ml–1 hydrazine sulphate, arsenite was twice extracted into 10 ml of chloroform. The arsenite in the combined chloroform was then back extracted to 10 ml of diluted hydrochloric acid. Subsequently, the organic matters were destructed by dryashing at 425°C for 12 h. The resulting ash was dissolved in a solution of 0.5 ml water and 5 ml of concentrated hydrochloric acid. For quality control, quality control reference material was purchased from the Food Analysis Performance Assessment Scheme (FAPAS).
652
S.W-c Chung et al.
Table 1. Total As and iAs contents (μg kg–1) in food groups of the first Hong Kong TDS. iAs
Downloaded by [Uppsala universitetsbibliotek] at 09:26 14 October 2014
Food group
Total As
Percentage of Percentage of Number of composite composite Mean ± SD composite samples samples < LOD (μg kg–1)a [Range] samples < LOD
Cereals and their products Vegetables and their products Legumes, nuts and seeds and their products Fruits Meat, poultry and game and their products Eggs and their products Fish and seafood and their products Dairy products Fats and oils Beverages, alcoholic Beverages, non-alcoholic Mixed dishes Snack foods Sugars and confectionery Condiments, sauces and herbs Total
Mean ± SD (μg kg–1)a
[Range]
76 140
29 49
8 ± 10 9 ± 16
[n.d.–46] [n.d.–120]
21 41
16 ± 19 12 ± 22
[n.d.–79] [n.d.–140]
24
63
4±4
[n.d.–14]
38
13 ± 16
[n.d.–68]
68 48
78 54
4 ± 11 4±5
[n.d.–88] [n.d.–27]
62 2
6 ± 18 29 ± 24
[n.d.–150] [n.d.–130]
12 76
33 17
23 ± 30 15 ± 15
[n.d.–93] [n.d.–74]
25 0
37 ± 41 1900 ± 2700
[n.d.–110] [6–14000]
20 8 8 40 48 4 8 20
100 100 50 95 21 0 63 40
1.5 1.5 4±2 2±2 6±4 8±2 3±3 8 ± 14
[n.d.] [n.d.] [n.d.–7] [n.d.–12] [n.d.–19] [6–10] [n.d.–8] [n.d.–65]
60 38 13 73 0 0 50 20
600
49
3 6 5 2 82 25 9 47
± ± ± ± ± ± ± ±
3 6 3 2 116 8 10 83
[n.d.–10] [n.d.–19] [n.d.–9] [n.d.–20] [4–500] [13–32] [n.d.–24] [n.d.–280]
30
Note: aHalf of the LOD is used for all results less than the LOD in calculating the mean concentration. n.d. denotes non-detected, i.e. results less than the LOD.
The analytical quantification of iAs was performed using hydride generation inductively coupled plasma mass spectrometry (Agilent ICP-MS 7500-Ce). The power was set at 1500 W. Carrier gas and makeup gas were set at 0.3 and 1 L min–1 respectively. The spray chamber was cooled to 2°C. Sample flow and NaBH4 solution flow were set at 0.3 and 0.1 rps respectively. 75As was quantified with correction of m/z 77 and 82 signals as described in US EPA method 6020A (2007). Five points calibration curve was established from 0 to 10 μg l–1, equivalent to a working range from LOD to 100 μg kg–1. (This procedure was also known to extract a small amount of monomethylarsenic species; FSA 2009a.) For the comparison of the measured and referenced concentrations of iAs, each test run included spiked test samples and quality control (QC) reference material (T0792 seaweed). The LOD and LOQ of iAs are 3 and 10 μg kg–1 in food, and 1.5 and 5 μg kg–1 in drinking water and bottled water. Recovery percentages based on FAPAS’s quality control reference material ranged between 89 and 122. The average spiking recovery percentages for ongoing performance were 87% (< 7% RSD).
Results and discussion Total As content in food items For the 600 TDS samples analysed, total As was detected in 418 samples and the results for 15 food groups are
summarised in Table 1. As expected, the highest mean total As level was detected in food group ‘fish and seafood and their products’ (mean of 1900 μg kg–1). The second highest food group was ‘mixed dish’ (mean of 82 μg kg–1) and followed by ‘condiments, sauces and herbs’ (mean of 47 μg kg–1) and ‘eggs and their products’ (mean of 37 μg kg–1). Compared with the UK TDS conducted in 2006 (FSA 2009b), the mean level of the second to fourth highest food groups obtained in this study is higher than the second highest food group of poultry in the UK. It is not surprising that ‘mixed dish’ was found to contain high total As since most of these dishes had either shrimp and/or pork as an ingredient. For ‘condiments, sauces and herbs’ the main source of total As came from oyster sauce, while other food items have almost an total As content a magnitude order lower. Amongst ‘eggs and their products’ salted and preserved duck eggs are major contributors while total As was not detected in chicken eggs. A total of 30 food items were found to contain nondetectable amount of total As, including corn, Chineseor Japanese-style noodles, oatmeal, carrot/radish, potato, broccoli, European variety cabbage, European lettuce, hairy gourd, pumpkin, wax gourd, zucchini, sweet pepper, tomato, green string beans with pod, mung bean vermicelli, dragon fruit, orange, watermelon, whole milk, skim milk, milk tea, coffee, soybean drink, carbonated drink, bottled distilled water, drinking water, granulated white sugar, and table salt. Similar findings
Food Additives & Contaminants: Part A
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for vegetables/fruits were reported in the TDS of Australia (2002), US Food and Drug Administration (2010) and Fontcuberta et al. (2011). iAs content in food items Among the 600 iAs results, 51% of the samples were found to contain detectable amounts (Table 1). The highest iAs level was detected in the food group ‘eggs and their products’ (mean of 23 μg kg–1), followed by ‘fish and seafood and their products’ (mean of 15 μg kg–1), and ‘vegetables and their products’ (mean of 9 μg kg–1). The majority (95%) of non-alcoholic beverage samples and all samples of ‘dairy products’ and ‘fats and oils’ were not contaminated with iAs. Among the 150 food items, water spinach was found to contain the highest level (mean of 74 μg kg–1, range of 35–120 μg kg–1), followed by salted eggs (mean of 58 μg kg–1) and oyster (mean of 58 μg kg–1). Although the literature has reported that water is one of the most significant sources of inorganic As exposure (WHO 2003; JECFA 2011), no water sample from this study contained detectable iAs. Besides, 22 food items were also found to contain a detectable amount of total As but not iAs, including western-style pasta, pastries, bean curd, kiwi fruit, peach, pear, plum, mutton, pork, soy sauce, chicken, roasted duck/goose, chicken egg, mandarin fish, grass carp fish, cheese, yogurt, ice-cream, butter, vegetable oil, tea, malt drink, and chrysanthemum tea. Ratios of total As and iAs content in foods Since individual samples of food items under the mixed dishes subgroup were composed of different ingredients and contents, these food items are excluded from the discussion. Those food items with more than two out of the four composite samples found to contain non-detectable iAs were also excluded from the discussion. The average As levels and percentage of iAs of the remaining 69 food items are summarised in Table 2. The average As values were calculated based on medium-bound values, i.e. 0.5 LOD was used for the calculation in case of ‘not detected’. In order to show that one or two of the four composite samples were found to contain non-detectable iAs, ‘0%’ is listed as the lower range of the ratio. To avoid anomalous percentage results, composite samples with both non-detectable total As and iAs were excluded from the ratio calculation. The mean ratio of iAs to total As for food items was found to be lowest in ‘fish, seafood and their products’ and ranged from 0.2% to 9.4%. This agrees with previous findings (Rattanachongkiat et al. 2004; Peshut et al. 2008; Sirot et al. 2009) of
Food Additives & Contaminants: Part A Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tfac20
Total and inorganic arsenic in foods of the first Hong Kong total diet study a
a
a
Stephen Wai-cheung Chung , Chi-ho Lam & Benny Tsz-pun Chan a
Food Research Laboratory, Food and Environmental Hygiene Department, Centre for Food Safety, Hong Kong, China Accepted author version posted online: 19 Dec 2013.Published online: 24 Feb 2014.
To cite this article: Stephen Wai-cheung Chung, Chi-ho Lam & Benny Tsz-pun Chan (2014) Total and inorganic arsenic in foods of the first Hong Kong total diet study, Food Additives & Contaminants: Part A, 31:4, 650-657, DOI: 10.1080/19440049.2013.877162 To link to this article: http://dx.doi.org/10.1080/19440049.2013.877162
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Food Additives & Contaminants: Part A, 2014 Vol. 31, No. 4, 650–657, http://dx.doi.org/10.1080/19440049.2013.877162
Total and inorganic arsenic in foods of the first Hong Kong total diet study Stephen Wai-cheung Chung*, Chi-ho Lam and Benny Tsz-pun Chan Food Research Laboratory, Food and Environmental Hygiene Department, Centre for Food Safety, Hong Kong, China
Downloaded by [Uppsala universitetsbibliotek] at 09:26 14 October 2014
(Received 17 September 2013; accepted 12 December 2013) Arsenic (As) is a metalloid that occurs in different inorganic and organic forms, which are found in the environment from both natural occurrence and anthropogenic activity. The inorganic forms of As (iAs) are more toxic as compared with the organic As, but so far most of the occurrence data in food collected in the framework of official food control are still reported as total As without differentiating the various As species. In this paper, total As and iAs contents of 600 total diet study (TDS) samples, subdivided into 15 different food groups, were quantified by high-resolution inductively coupled plasma mass spectrometry (HR-ICP/MS) and hydride generation (HG) ICP/MS respectively. The method detection limits for both total As and iAs were 3 μg As kg−1. As the samples were prepared for TDS, food items were purchased directly from the market or prepared as for normal consumption, i.e. table ready, in the manner most representative of and consistent with cultural habits in Hong Kong as far as practicable. The highest total As and iAs content were found in ‘fish, seafood and their products’ and ‘vegetables and their products’ respectively. Besides, this paper also presents the ratios of iAs and total As content in different ready-to-eat food items. The highest ratio of iAs to total As was found in ‘vegetables and their products’. It is likely that iAs in vegetables maintained its status even after cooking. Keywords: total arsenic; inorganic arsenic; total diet study; ready-to-eat food items
Introduction Arsenic (As) is a metalloid that occurs in inorganic and organic forms and is found in the environment from both natural sources and human activities (Eisler 2000; JECFA 2011). Inorganic arsenic (iAs), including trivalent and pentavalent As, is the more toxic form of As; it may cause cancers of the urinary bladder, lung and skin, skin lesions, cardiovascular disease, neurotoxicity and diabetes (EFSA 2009; IARC 2009; JECFA 2011). Even though the toxicity of trivalent As is the highest amongst all the possible chemical species of this element, JECFA only determined the iAs benchmark dose lower confidence limit for a 0.5% increased incidence of lung cancer in humans (BMDL0.5) as 3.0 μg kg–1 body weight (bw) day–1 (in the region of 2–7 μg kg–1 bw day–1) in 2010. Therefore, there is no need to distinguish the trivalent and pentavalent As for dietary exposure studies. Intake of low levels of iAs may be unavoidable due to its ubiquitous nature and food is also recognised as the major source of iAs exposure (WHO 2003; EFSA 2009; JECFA 2011). Foods and beverages usually contain iAs at levels not exceeding 100 μg kg–1 with mean values generally less than 30 μg kg–1. However, seaweed, rice, and some fish and seafood commodities, as well as food crops grown in As-contaminated soils, may have higher iAs levels and their proportions of iAs to the total As also vary a lot (Codex 2011; JECFA 2011). *Corresponding author. Email: [email protected] © 2014 Taylor & Francis
In the Scientific Opinion from EFSA on As in food, approximately 98% of the submitted results from 15 European countries were reported as total As, and only a few investigations differentiated between the various As species. Besides, the EFSA Panel on Contaminants in the Food Chain was not able to assess the typical ratios between inorganic and organic As in different groups of foodstuffs as representative speciation data were scarce. Thus, the proportion of iAs was assumed to vary from 50% to 100% of the total As reported in food commodities other than fish and seafood, with 70% considered as best reflecting an overall average. In fish and seafood the relative proportion of iAs is small and tends to decrease as the total As content increases, and the ratio may vary depending on the seafood type. Moreover, iAs content may vary after the cooking process (Diaz et al. 2004; Devesa et al. 2008). The total diet study (TDS) has been recognised internationally as the most cost-effective way to estimate the dietary exposures to food chemicals for various population groups and to assess their associated health risks, and it provides a scientific basis for assessing food safety risks and regulating food supply (WHO 2005). In 2010, the Centre for Food Safety (CFS) started to conduct the first Hong Kong TDS, aiming to estimate dietary exposures of the Hong Kong population and various population subgroups to a range of substances, including contaminants and nutrients, and thus assess any associated health risk.
Food Additives & Contaminants: Part A In view of the differences of associated health risk between iAs and total As and limited speciation data, this paper aims to present the results of both iAs and total As contents in 150 TDS food items.
Materials and methods
Downloaded by [Uppsala universitetsbibliotek] at 09:26 14 October 2014
Food selection and sampling The latest and most comprehensive food consumption data from the Hong Kong Population-based Food Consumption Survey (FCS) were used. The FCS was conducted by CFS in 2005–07 among 5008 Hong Kong adults aged between 20 and 84 years by means of two non-consecutive 24-h dietary intake questionnaires supplemented by a food-frequency questionnaire. It revealed that over 1400 food items were consumed by the Hong Kong population (FEHD 2010). A total of 150 TDS food items were selected for the study, based on the food consumption data captured from the FCS, representing 88% of the daily ration of the average individual. Food sampling was conducted on four occasions over 1 year from March 2010 to February 2011. On each occasion three samples of each TDS food item were purchased from various retail outlets in different regions of the territory, namely Kowloon, Hong Kong Island and New Territories, and prepared as for normal consumption, i.e. table ready, in a manner most representative of and consistent with cultural habits in Hong Kong as far as practicable. Samples were brought on the same day of collection and kept for not more than 1 day in the refrigerator until sample preparation. A total of 1800 samples were collected.
Sample preparation Samples were prepared according to the standard procedures. They were then homogenised individually and combined into a composite sample. A total of 1800 samples were collected and combined into 600 composite samples. Distilled water was used for food preparation, and no salt and cooking oil were added during food preparation (FEHD 2012). Samples prepared were kept at −18°C and transferred to the laboratory for analysis as soon as possible (normally less than 3 h). The equipment used for preparing and homogenising the composite samples was thoroughly washed between each preparation (e.g. cleaning with a laboratory-grade detergent, rinsing thoroughly with hot tap water and rinsing thoroughly with deionised water) to avoid the risk of cross-contamination.
Analytical determination of total As Total As was extracted by microwave-assisted concentrated nitric acid digestion of the sample, followed by high-resolution inductively coupled plasma mass
651
spectrometry (HR-ICP/MS) determination. In brief, the composite samples (2 g) were digested in 10 ml concentrated nitric acid using Teflon high-pressure closed vessels and microwave heating for 40 min. The digestion was carried out with a four-step programme ramping from 200 psi/75°C to 500 psi/180°C at a constant power of 1200 W. The digest was diluted to 50 ml with water. The sample solution was filtered and spiked with internal standard before instrument analysis. The analytical quantification of total As was achieved by HR-ICP/MS (Thermo Element 2, Bremen, Germany), equipped with concentric nebuliser, quartz double-pass spray chamber (cooled to 2°C), and platinum skimmer and sample cone. Power was set at 1255 W. The peristaltic pump speed and sample take-up speed were set at 10 rpm and 0.5 ml min–1, respectively. Cool gas, auxiliary gas and sample gas were set at 16, 1 and 1 L min–1 respectively. Resolution was set as high, which means the resolution of 115In was at least 10 000. 75As was monitored for quantitation; 72Ge was used as the internal standard (IS). The calibration curve was established by 11 concentration levels range of 0 to 100 μg l–1 (with an IS concentration of 5 μg l–1), which a working range of LOD–2500 μg kg–1. LODs and LOQs were 3 and 15 μg kg–1 in food, and 0.6 and 3 μg kg–1 in drinking water and bottled water, respectively. For quality control, a number of CRMs were used and included typical diet (NIST SRM1548a), oyster tissue (NIST SRM1566b), rice flour (NIST SRM1568a), spinach leaf (NIST SRM1570a), bovine liver (NIST SRM1577c) and lobster hepatopancreas (NRC TORT-2). All CRMs were used as provided without further grinding. CRMs were stored under the same conditions and digested with the same protocol as the analysed food samples. The average recovery percentages of CRMs range of 97% to 123% with %RSD < 7.5%. The average spiking recovery percentage for ongoing performance monitoring was 103% (< 5% RSD). Analytical determination of iAs iAs refers to the sum of arsenite (As(III)) and arsenate (As (V)). The composite samples (2.5 g) were solubilised in around 3 ml deionised water and 18.4 ml concentrated hydrochloric acid. After reduction with 2 ml of hydrogen bromide and 1 ml of 15 mg ml–1 hydrazine sulphate, arsenite was twice extracted into 10 ml of chloroform. The arsenite in the combined chloroform was then back extracted to 10 ml of diluted hydrochloric acid. Subsequently, the organic matters were destructed by dryashing at 425°C for 12 h. The resulting ash was dissolved in a solution of 0.5 ml water and 5 ml of concentrated hydrochloric acid. For quality control, quality control reference material was purchased from the Food Analysis Performance Assessment Scheme (FAPAS).
652
S.W-c Chung et al.
Table 1. Total As and iAs contents (μg kg–1) in food groups of the first Hong Kong TDS. iAs
Downloaded by [Uppsala universitetsbibliotek] at 09:26 14 October 2014
Food group
Total As
Percentage of Percentage of Number of composite composite Mean ± SD composite samples samples < LOD (μg kg–1)a [Range] samples < LOD
Cereals and their products Vegetables and their products Legumes, nuts and seeds and their products Fruits Meat, poultry and game and their products Eggs and their products Fish and seafood and their products Dairy products Fats and oils Beverages, alcoholic Beverages, non-alcoholic Mixed dishes Snack foods Sugars and confectionery Condiments, sauces and herbs Total
Mean ± SD (μg kg–1)a
[Range]
76 140
29 49
8 ± 10 9 ± 16
[n.d.–46] [n.d.–120]
21 41
16 ± 19 12 ± 22
[n.d.–79] [n.d.–140]
24
63
4±4
[n.d.–14]
38
13 ± 16
[n.d.–68]
68 48
78 54
4 ± 11 4±5
[n.d.–88] [n.d.–27]
62 2
6 ± 18 29 ± 24
[n.d.–150] [n.d.–130]
12 76
33 17
23 ± 30 15 ± 15
[n.d.–93] [n.d.–74]
25 0
37 ± 41 1900 ± 2700
[n.d.–110] [6–14000]
20 8 8 40 48 4 8 20
100 100 50 95 21 0 63 40
1.5 1.5 4±2 2±2 6±4 8±2 3±3 8 ± 14
[n.d.] [n.d.] [n.d.–7] [n.d.–12] [n.d.–19] [6–10] [n.d.–8] [n.d.–65]
60 38 13 73 0 0 50 20
600
49
3 6 5 2 82 25 9 47
± ± ± ± ± ± ± ±
3 6 3 2 116 8 10 83
[n.d.–10] [n.d.–19] [n.d.–9] [n.d.–20] [4–500] [13–32] [n.d.–24] [n.d.–280]
30
Note: aHalf of the LOD is used for all results less than the LOD in calculating the mean concentration. n.d. denotes non-detected, i.e. results less than the LOD.
The analytical quantification of iAs was performed using hydride generation inductively coupled plasma mass spectrometry (Agilent ICP-MS 7500-Ce). The power was set at 1500 W. Carrier gas and makeup gas were set at 0.3 and 1 L min–1 respectively. The spray chamber was cooled to 2°C. Sample flow and NaBH4 solution flow were set at 0.3 and 0.1 rps respectively. 75As was quantified with correction of m/z 77 and 82 signals as described in US EPA method 6020A (2007). Five points calibration curve was established from 0 to 10 μg l–1, equivalent to a working range from LOD to 100 μg kg–1. (This procedure was also known to extract a small amount of monomethylarsenic species; FSA 2009a.) For the comparison of the measured and referenced concentrations of iAs, each test run included spiked test samples and quality control (QC) reference material (T0792 seaweed). The LOD and LOQ of iAs are 3 and 10 μg kg–1 in food, and 1.5 and 5 μg kg–1 in drinking water and bottled water. Recovery percentages based on FAPAS’s quality control reference material ranged between 89 and 122. The average spiking recovery percentages for ongoing performance were 87% (< 7% RSD).
Results and discussion Total As content in food items For the 600 TDS samples analysed, total As was detected in 418 samples and the results for 15 food groups are
summarised in Table 1. As expected, the highest mean total As level was detected in food group ‘fish and seafood and their products’ (mean of 1900 μg kg–1). The second highest food group was ‘mixed dish’ (mean of 82 μg kg–1) and followed by ‘condiments, sauces and herbs’ (mean of 47 μg kg–1) and ‘eggs and their products’ (mean of 37 μg kg–1). Compared with the UK TDS conducted in 2006 (FSA 2009b), the mean level of the second to fourth highest food groups obtained in this study is higher than the second highest food group of poultry in the UK. It is not surprising that ‘mixed dish’ was found to contain high total As since most of these dishes had either shrimp and/or pork as an ingredient. For ‘condiments, sauces and herbs’ the main source of total As came from oyster sauce, while other food items have almost an total As content a magnitude order lower. Amongst ‘eggs and their products’ salted and preserved duck eggs are major contributors while total As was not detected in chicken eggs. A total of 30 food items were found to contain nondetectable amount of total As, including corn, Chineseor Japanese-style noodles, oatmeal, carrot/radish, potato, broccoli, European variety cabbage, European lettuce, hairy gourd, pumpkin, wax gourd, zucchini, sweet pepper, tomato, green string beans with pod, mung bean vermicelli, dragon fruit, orange, watermelon, whole milk, skim milk, milk tea, coffee, soybean drink, carbonated drink, bottled distilled water, drinking water, granulated white sugar, and table salt. Similar findings
Food Additives & Contaminants: Part A
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for vegetables/fruits were reported in the TDS of Australia (2002), US Food and Drug Administration (2010) and Fontcuberta et al. (2011). iAs content in food items Among the 600 iAs results, 51% of the samples were found to contain detectable amounts (Table 1). The highest iAs level was detected in the food group ‘eggs and their products’ (mean of 23 μg kg–1), followed by ‘fish and seafood and their products’ (mean of 15 μg kg–1), and ‘vegetables and their products’ (mean of 9 μg kg–1). The majority (95%) of non-alcoholic beverage samples and all samples of ‘dairy products’ and ‘fats and oils’ were not contaminated with iAs. Among the 150 food items, water spinach was found to contain the highest level (mean of 74 μg kg–1, range of 35–120 μg kg–1), followed by salted eggs (mean of 58 μg kg–1) and oyster (mean of 58 μg kg–1). Although the literature has reported that water is one of the most significant sources of inorganic As exposure (WHO 2003; JECFA 2011), no water sample from this study contained detectable iAs. Besides, 22 food items were also found to contain a detectable amount of total As but not iAs, including western-style pasta, pastries, bean curd, kiwi fruit, peach, pear, plum, mutton, pork, soy sauce, chicken, roasted duck/goose, chicken egg, mandarin fish, grass carp fish, cheese, yogurt, ice-cream, butter, vegetable oil, tea, malt drink, and chrysanthemum tea. Ratios of total As and iAs content in foods Since individual samples of food items under the mixed dishes subgroup were composed of different ingredients and contents, these food items are excluded from the discussion. Those food items with more than two out of the four composite samples found to contain non-detectable iAs were also excluded from the discussion. The average As levels and percentage of iAs of the remaining 69 food items are summarised in Table 2. The average As values were calculated based on medium-bound values, i.e. 0.5 LOD was used for the calculation in case of ‘not detected’. In order to show that one or two of the four composite samples were found to contain non-detectable iAs, ‘0%’ is listed as the lower range of the ratio. To avoid anomalous percentage results, composite samples with both non-detectable total As and iAs were excluded from the ratio calculation. The mean ratio of iAs to total As for food items was found to be lowest in ‘fish, seafood and their products’ and ranged from 0.2% to 9.4%. This agrees with previous findings (Rattanachongkiat et al. 2004; Peshut et al. 2008; Sirot et al. 2009) of
