- Email: [email protected]
A Market Basket Survey of Inorganic Arsenic in Food
Food and Chemical Toxicology 37 (1999) 839±846
www.elsevier.com/locate/foodchemtox
Research Section
A Market Basket Survey of Inorganic Arsenic in Food R. A. SCHOOF1*, L. J. YOST1, J. EICKHOFF2, E. A. CRECELIUS3, D. W. CRAGIN4, D. M. MEACHER5 and D. B. MENZEL5 Exponent, Bellevue, WA, 2ENVIRON, Arlington, VA, 3Battelle Marine Sciences, Sequim, WA, 4Elf Atochem North America, Inc., Philadelphia, PA and 5University of California, Irvine, CA, USA
1
(Accepted 7 February 1999) AbstractÐDietary arsenic intake estimates based on surveys of total arsenic concentrations appear to be dominated by intake of the relatively non-toxic, organic arsenic forms found in seafood. Concentrations of inorganic arsenic in food have not been not well characterized. Accurate dietary intake estimates for inorganic arsenic are needed to support studies of arsenic's status as an essential nutrient, and to establish background levels of exposure to inorganic arsenic. In the market basket survey reported here, 40 commodities anticipated to provide at least 90% of dietary inorganic arsenic intake were identi®ed. Four samples of each commodity were collected. Total arsenic was analysed using an NaOH digestion and inductively coupled plasma±mass spectrometry. Separate aliquots were analysed for arsenic species using an HCl digestion and hydride atomic absorption spectroscopy. Consistent with earlier studies, total arsenic concentrations (all concentrations reported as elemental arsenic per tissue wet weight) were highest in the seafoods sampled (ranging from 160 ng/g in freshwater ®sh to 2360 ng/ g in saltwater ®sh). In contrast, average inorganic arsenic in seafood ranged from less than 1 ng/g to 2 ng/g. The highest inorganic arsenic values were found in raw rice (74 ng/g), followed by ¯our (11 ng/g), grape juice (9 ng/g) and cooked spinach (6 ng/g). Thus, grains and produce are expected to be signi®cant contributors to dietary inorganic arsenic intake. # 1999 Elsevier Science Ltd. All rights reserved Keywords: inorganic arsenic; dietary exposures; arsenic in food. Abbreviations: DMA = dimethylarsenic acid; MMA = monomethylarsonic acid.
INTRODUCTION
Arsenic has been detected in most foods tested. Although arsenic may be present in foods in a variety of organic compounds as well as in inorganic forms, most studies have reported only total arsenic concentrations. Based on studies in laboratory animals, inorganic arsenic may be a required nutrient for humans; however, the required intakes and the intakes from typical diets are not well characterized (Uthus, 1994a,b; Uthus and Seaborn, 1996). During the last two decades, much progress has been made in understanding the forms and concentrations of arsenic in some foods. The primary focus of prior research has been on arsenic in aquatic organisms, many of which contain total arsenic concentrations two to three orders of magnitude greater than total arsenic concentrations in foods of terrestrial origin *Corresponding author.
(Jelinek and Corneliussen, 1977; Schroeder and Balassa, 1966). Studies of the arsenic forms found in ®n®sh and shell®sh have demonstrated that most arsenic in these foods occurs as methylated arsenic compounds, with only small amounts of inorganic arsenic present (Buchet et al., 1994; Francesconi and Edmonds, 1994; Phillips, 1994; Yost et al., 1998). Inorganic arsenic is not formed after ingestion of these compounds (Buchet et al., 1994, 1996), indicating little or no metabolism in humans to the most toxic forms of arsenic. The complex arsenic compounds that predominate in marine organisms are much less acutely toxic than soluble inorganic arsenic compounds, with arsenobetaine (the predominant compound in ®n®sh) being virtually nontoxic (Shiomi, 1994; Yamauchi and Fowler, 1994). Monomethylarsonic (MMA) and dimethylarsenic (DMA) acids are also less acutely toxic than the
0278-6915/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. Printed in Great Britain PII S0278-6915(99)00073-3
840
R. A. Schoof et al.
inorganic forms, arsenite (As3+) and arsenate (As5+). The forms of arsenic present in foods of terrestrial origin are not well characterized, largely due to their occurrence at ng/g concentrations that are below the detection limits of many analytical methods. In contrast, the methylated arsenic forms in seafood, which occur at mg/g concentrations, have been much more thoroughly studied (Francesconi and Edmonds, 1994). Methylated arsenic compounds are much less prevalent in terrestrial food sources than in seafood. A recent report indicates that between 25 and 100% of total arsenic in terrestrial foods may be inorganic arsenic (Yost et al., 1998). Accurate estimates of the forms of arsenic in the diet are an important component of evaluations of background arsenic exposures and of possible nutritional status for this microelement. However, most dietary studies have reported only total arsenic concentrations. For example, recent diet studies that included evaluations of total arsenic in foods have been reported for Canada, the United States, and Japan (Dabeka et al., 1993; Gunderson, 1995; Tsuda et al., 1995). These studies used market basket survey techniques in which a large number of foods or food composites were tested, often after cooking, for total arsenic concentrations. Food consumption data were then used to estimate daily arsenic intakes. Daily intake estimates varied substantially among the three countries, from 38.6 mg total arsenic for young American men to 59.2 mg for a similar age group of Canadian men, with far higher values being reported for Japanese women (160 and 280 mg during two dierent years) (Dabeka et al., 1993; Gunderson, 1995; Tsuda et al., 1995). In all three countries, total arsenic intake was dominated by arsenic from seafood. Thus, the variations in daily arsenic intake among residents of dierent countries largely re¯ect variations in seafood consumption. Seafood accounted for almost 90% of daily arsenic intake in the United States (Gunderson, 1995), approximately 70% in Canada (Dabeka et al., 1993), and 60±70% in Japan (Tsuda et al., 1995). In Japan, an additional factor was consumption of seaweed and rice, which accounted for most of the remaining arsenic intake. Some indirect estimates of inorganic arsenic intakes can be made from the studies of total arsenic in the diet if seafood sources of arsenic are excluded (based on the assumption that almost all arsenic in seafood is organic, while arsenic in terrestrial foods is mostly inorganic). For example, in young American men, only 4.5 mg of daily arsenic intake was attributable to sources other than seafood (Gunderson, 1995). In young Canadian men, approximately 20 mg arsenic per day was from nonseafood sources (Dabeka et al., 1993).
Direct measurements of inorganic arsenic in diets are scanty. A duplicate diet study of Japanese adults reported an average daily inorganic arsenic intake of 13.7 mg when total arsenic intake was 202 mg (Mohri et al., 1990). A recent study suggests that typical North American diets contain less than 15 mg inorganic arsenic per day, but these estimates are considered preliminary due to the limited number of foods for which inorganic arsenic concentrations were available (Yost et al., 1998). The study reported here provides inorganic arsenic concentrations for a wide variety of foods, selected so that a market basket approach can be used to estimate inorganic arsenic intake from the diet.
MATERIALS AND METHODS
Market basket design and sample collection Food consumption data from the US Department of Agriculture Continuing Surveys of Food Intakes by Individuals (USDA, 1992, 1993, 1994), surveys of total arsenic in food (Dabeka et al., 1993; FDA, 1997), and estimates of inorganic arsenic concentrations in food (Yost et al., 1998) were used to select 40 commodities that were predicted to account for at least 90% of the dietary inorganic arsenic in the United States. The USDA consumption data were used to determine the foods consumed in the largest quantities. Total arsenic levels in foods from the total diet studies conducted in the United States and Canada were adjusted to re¯ect predicted inorganic arsenic levels and used to identify foods likely to have the highest inorganic arsenic levels. All foods thus identi®ed (high consumption and/or expected high levels of inorganic arsenic) were included in inorganic arsenic dietary intake analyses for the United States. The estimated intakes for the foods (consumption inorganic arsenic concentration) were ordered from highest to lowest; the foods that together contributed the top 90% of inorganic arsenic intake were selected for the market basket survey. A modi®ed market basket survey method was used to collect four samples of each commodity. The food samples were collected during October 1997 from large supermarkets in two towns in Texas, two samples each from Bryan and Tyler (except that the ``Tyler'' beer samples were collected in Coee City, Texas). Tap water was also included in the study; samples were collected in a hotel (Tyler samples) and in restaurants (Bryan samples). The food samples were prepared in accordance with Appendix B from Appendices for the 1990 Revision of the Food and Drug Administration's Total Diet Food List and Diets (Pennington, 1992), with some exceptions. Rice samples were not cooked (raw rice was tested to facilitate comparisons with arsenic concentrations reported in previous studies). Vegetables were cooked in a
Survey of inorganic arsenic in food
microwave oven, instead of being boiled in water. Commodities collected, a description of the samples, the state or country of origin of the raw commodity (if known), and a brief description of the preparation/cooking methods are presented in Table 1. Each sample was then analysed separately (i.e. no composites were prepared). Sample analyses All samples were analysed at Battelle Marine Sciences in Sequim, Washington. Total arsenic was analysed in food commodities after NaOH digestion by inductively coupled plasma±mass spectrometry (ICP±MS). Approximately one in every 10 samples was analysed in triplicate. For the digestion of liquids (milk, juices and water), NaOH was added to 8 g liquid to produce 2 N NaOH solution. This solution was heated for 16 hr at 808C. For the digestion of solid food, either 1 or 2 g food was digested in 13 ml 2 N NaOH for 16 hr at 808C. In preparation for ICP±MS analysis, 1 ml digestate was diluted with 9 ml 2% concentrated HNO3. A model Elan 5000 Perkin-Elmer ICP±MS was operated using the stock cross-¯ow nebulizer. Several ions were monitored to evaluate polyatomic interference from Ar40 Cl35, which has the same mass as arsenic. When interference occurred, the manufacturer's correction factor was used to reduce the interference. Food samples were digested for analysis of total arsenic using NaOH instead of HNO3, which had been used in a previous study of arsenic in rice and yams (Schoof et al., 1998). The NaOH digestion was expected to be more eective than HNO3 in dissolving food with high fat content. A comparison between these two types of digestions on ®ve dierent rice samples resulted in a relative percent dierence of 10% between the mean concentrations. Total arsenic results for oyster tissue digested with NaOH or HNO3 agreed within 5%. Analysis of standard reference bovine liver (certi®ed 0.055 mg/g As) digested with NaOH resulted in 0.071 mg/g and digested with HNO3 resulted in 0.062 mg/g. These results indicate that both digestion methods are comparable and accurate. Arsenic speciation was determined in food samples digested with HCl. Between 0.5 and 2 g of food was digested with 13 ml 2 N HCl at 808C for 16 hr. The digestates were stored at 48C before analysis by EPA Method 1632, (US EPA, 1996). A 2-ml aliquot of the digestate was analysed for As3+ by arsine generation at pH 6 with the reducing agent sodium borohydride. The hydride was collected on a cryogenic column before quanti®cation by atomic absorption (AA) using a quartz tube with an air±hydrogen ¯ame positioned in the light path. The HCl digestion is eective in dissolving the arsenic compounds in food without changing the oxidative states of As3+ and As5+ (Beauchemin
841
et al., 1988; Schoof et al., 1998). Also, MMA and DMA are not decomposed during the digestion. Recovery of matrix spikes of As3+, As5+, MMA and DMA added to 21 dierent foods indicates that the digestion process does not alter the speciation of these four compounds. Mean spike recoveries for the four arsenic species were 92% for As3+, 86% for As5+, 89% for MMA and 98% for DMA. Because there are few published data on arsenic speciation in food, comparisons with other digestion methods are limited. The Canadian National Research Council reported the certi®ed reference material DORM-1 (dog®sh muscle) contained 0.472 0.02 mg/g DMA (Beauchemin et al., 1988). Our results for seven replicates of DORM-1, analysed with dierent batches of food, had a mean and standard deviation of 0.56 2 0.07 mg/g. The concentrations of arsenic species were stable for over 1 month in the digestates of certi®ed reference materials stored at 48C. The quanti®cation of total inorganic arsenic, MMA and DMA was conducted similarly to that of As3+, except that arsines were generated at pH 1. The three arsines (arsine, methylarsine and dimethylarsine) were collected on the cold column, then quanti®ed by AA when the column was heated. The dierent column retention times of the arsines allows quanti®cation of inorganic arsenic, MMA and DMA. The concentration of As5+ is determined by the dierence between inorganic arsenic and As3+. Every fourth sample was analysed in triplicate. The data were blank-corrected by subtracting the mean of the procedural blanks. The mean blank concentrations are shown in Table 2. The method detection limits were determined from the variance in triplicate analyses of food samples containing low but detectable arsenic. The standard deviation was multiplied by the Student's t-value for 95% con®dence level. The method detection limits are shown in Table 2. If no arsenic was detected (after blank correcting), one-half the value of the method detection limit was given with a ``U '' ¯ag. One-half the detection limit was used in subsequent calculations. Mean values have a ``U '' quali®er if all values used to calculate the mean were ``U '' quali®ed. When the concentration of arsenic in food (after blank correcting) was detected above the blank concentration but below the method detection limit, the value was ``J'' ¯agged. The same rule as was used for the ``U'' ¯agged values was also applied in assigning ``J'' quali®ers to mean values. RESULTS
Table 3 shows mean concentrations of total and inorganic arsenic for 40 commodities and tap water. The data from the two towns from which food samples were collected did not dier signi®cantly.
842
R. A. Schoof et al. Table 1. Commodities tested: description and preparation method
Food Fats, oils, sweets Sugar (beet) Sugar (cane) Corn syrup Butter Soybean oil Salt Beer Milk, yogurt, cheese Milk, skim Milk, whole Meat, poultry, ®sh, eggs, nuts Beef Chicken Pork Eggs Saltwater ®n®sh Tuna Freshwater ®n®sh Shrimp Peanut butter Vegetables Beans (green) Carrots Corn (kernel) Cucumber Lettuce Onions Peas Potatoes Spinach Tomato Fruit Apple, raw Apple, juice Banana Grapes Grape juice Orange Orange juice Peaches Watermelon Bread, cereal, rice, pasta Corn (meal) Flour (wheat) Rice Water Tap water 1
Sample description (origin)1
Preparation method
Granulated sugar (unknown) Granulated sugar (unknown) Light corn syrup (unknown) Unsalted sweet cream butter (1 Illinois, 2 Minnesota, 1 Ohio) Soybean/vegetable oil (unknown) Iodized salt (unknown) Bottled beer (2 Texas, 2 Missouri)
As As As As
Vitamin A & D skim milk (1 Ohio, 1 Texas, 2 Utah) Vitamin D whole milk (1 Ohio, 1 Texas, 2 Utah)
As is
Top sirloin steak (1 Texas, 3 unknown) Split chicken breasts with rib (1 Georgia, 1 Texas, 2 unknown) Pork loin chops (2 Minnesota, 1 Ohio, 1 Texas) Large, grade A eggs (2 Texas, 2 unknown) Orange roughy ®llet [1], cod ®llet [2], halibut steak [1] (unknown) Chunk light tuna packed in water (unknown) Cat®sh ®llet [3], rainbow trout [1] (1 Texas, 2 unknown, 1 Idaho) Shrimp (1 Gulf of Mexico, 1 Mexico, 2 unknown) Creamy peanut butter (unknown) Cut/frozen green beans (1 Wisconsin, 1 Minnesota, 1 unknown, 1 Tennessee) Bagged/loose carrots (2 Colorado, 1 California, 1 unknown) Cut/frozen whole kernel corn (1 Ohio, 2 Wisconsin, 1 unknown) Cucumber (unknown) Iceberg head lettuce/salad (4 California) Yellow/white onions(2 Colorado, 2 unknown) Frozen peas (1 Minnesota, 2 Wisconsin, 1 unknown) Russet/Idaho/long potatoes (1 California, 1 Idaho, 1 Washington, 1 unknown) Frozen chopped/cut leaf spinach (2 Georgia, 1 Wisconsin, 1 unknown) Roma/vine-ripened tomatoes (3 California, 1 Mexico) Red delicious/Jonathon/McIntosh apples (2 Washington, 1 Michigan, 1 Missouri) Apple juice (1 US, 1 Washington, 1 Hungary, 1 unknown) Banana (4 Guatemala) Red/green Thompson seedless grapes (3 California, 1 Nicaragua) Grape juice (2 US, 2 unknown) Navel/Valencia oranges (1 New Mexico, 2 Texas, 1 Australia) Frozen concentrated orange juice (4 US/Brazil mixture) Peaches from mixed fruit/frozen peaches (unknown) Cut watermelon/seedless/fresh watermelon (1 New Mexico, 1 Mexico, 2 unknown)
is is is is
As is As is As is
As is
Baked 30 min at 3508F Baked (with skin) until done at 3508F Baked 30 min at 3508F Peeled, boiled 3 min Baked 15±25 min at 3508±4008F Drained Baked (bones removed) until done microwaved (shelled) As is Microwaved 6±12 min (no water added) Peeled, microwaved 4±8 min (ends removed) Microwaved 6±7 min (no water added) Peeled (ends removed) Washed (individual leaves), drained Peeled (®rst layer removed) Microwaved 4±6 min (no water added) Peeled, some chopped, microwaved 10 min or until tender Microwaved 4±6 min Washed (skin left on)
Washed, peeled, cored (skin left on) As is (single strength) Peeled Washed in cool water, stems removed As is (single strength) Peeled, excess white membrane and seeds removed As is (concentrated) As is Rind and most seeds removed
Enriched/stone-ground/all-purpose/degerminated corn meal (2 unknown, 2 Texas) Graham/whole wheat ¯our (unknown- US) Long grain enriched rice (1 unknown, 3 Texas)
As is
Local taps/drink dispenser
As is (ran tap for 2 min)
The state or country where the raw commodity was produced is listed when known
As is As is (uncooked)
Survey of inorganic arsenic in food Table 2. Mean blank concentrations and method detection limits (ng/g wet weight)
Astot Asi As+3 As+5 MMA DMA
Mean blank concentrations
Method detection limits
4.57 1.96 <1 1.96 <1 <2
3.6 2 1 2 1 2
Note: Astot-total arsenic Asi-inorganic arsenic MMA-monomethylarsonic acid DMA-dimethylarsinic acid.
Consequently, the data for all four samples of each commodity were averaged. Total arsenic was detected in two or more samples of 35 of the 40 commodities, that is, all of the commodities except butter, soybean/vegetable oil, salt, whole milk and green beans. Inorganic arsenic was detected in two or more samples of 34 of the 40 commodities, that is, all commodities except soybean/vegetable oil, whole and skim milk, chicken, tuna and orange juice. Inorganic arsenic concentrations were either undetected or ``J`` quali®ed in approximately one-half of the samples, suggesting that the detection limits achieved in this study are just sucient to characterize inorganic arsenic concentrations in a wide variety of foods. Consistent with earlier studies, total arsenic concentrations (all concentrations reported as elemental arsenic per tissue wet weight) were highest in the four kinds of seafood sampled (means ranged from 160 ng/g in freshwater ®sh to 2360 ng/g in saltwater ®sh). In contrast, average inorganic arsenic mean concentrations in seafood ranged from less than 1 ng/g to 2 ng/g. Marked variation in total arsenic concentrations observed in ®n®sh samples may re¯ect variations among species (Table 4). Concentrations were more consistent among canned tuna samples. The next highest total arsenic concentrations occurred in rice (303 ng/g), which also had the highest concentrations of inorganic arsenic (Table 3). Other foods with relatively high (i.e. greater than 10 ng/g) total arsenic concentrations included foods high in protein (i.e. beef, chicken, pork, eggs and peanut butter) or sugar (i.e. beet sugar, cane sugar, grapes and grape juice), and grains (i.e. corn meal and ¯our). The inorganic arsenic concentrations in raw rice (74 ng/g) were much higher than concentrations in other foods. The next highest concentrations of inorganic arsenic were in ¯our (11 ng/g), grape juice (9 ng/g), cooked spinach (6 ng/g), peanut butter (5 ng/g), peas (5 ng/g), as well as cane sugar, corn meal, cucumber and beet sugar (all 4 ng/g). Inorganic arsenic concentrations were low enough in most foods that it was not clear what arsenic forms predominated (i.e. As3+ or As5+); however,
843
in rice, ¯our, grape juice, spinach, peanut butter and cucumber, the concentrations of As3+ were generally more than twice the concentration of As5+. In contrast, cane sugar and beet sugar appeared to have more As5+ than As3+ (data not shown). In fruits and vegetables, inorganic arsenic accounted for approximately one-half of the total arsenic (Table 3). In grains, sugars and oil, inorganic arsenic accounted for approximately onequarter of the total arsenic, while only a small fraction of the total was inorganic in meat, poultry, ®sh and eggs. With a few exceptions, both MMA and DMA concentrations were undetected or very low. Rice and shell®sh (shrimp) were the commodities with the highest DMA concentrations, with mean concentrations of 91 and 34 ng/g, respectively (Table 4). The next highest concentrations of DMA were in beet sugar and cane sugar, with concentrations of 7 and 8 ng/g, respectively (data not shown). DMA was also detected at low concentrations in seafood (Table 4), meat and fruits and fruit juices (data not shown). MMA was repeatedly detected only in samples of apple juice (data not shown) and rice (Table 4). DISCUSSION
Inorganic arsenic was found at ng/g concentrations in most foods tested. Concentrations for inorganic arsenic reported in the present study were generally lower than those previously reported for seafood, meat and poultry, even though total arsenic concentrations were similar among studies. For example, while inorganic arsenic concentrations in saltwater ®n®sh (cod, halibut, orange roughy, canned tuna) were less than 1 ng/g in the present study, three previous studies reported values from 5 to 28 ng/g for similar ®sh species (Buchet et al., 1994, Mohri et al., 1990; Yost et al., 1998). Similarly, inorganic arsenic concentrations in shrimp ranged from 1 to 3 ng/g in the four samples tested in the present study, compared to values of 37 ng/g (Mohri et al., 1990) and 100 ng/g (Yost et al., 1998) in two samples tested previously. Meat and poultry products tested in the present study (N = 12) also contained 1 ng/g or less of inorganic arsenic, compared to 9 to 24 ng/g reported in a previous study (Yost et al., 1998). Inorganic arsenic concentrations in other foods were generally consistent with previously reported values. Inorganic arsenic concentrations have been notably consistent among rice samples tested by several methods, with average values ranging from 74 to 110 ng/g (Table 5). In particular, similar concentrations were reported for split samples analysed by hydride AA after HCl digestion or by ICP±MS after a water-based extraction (Table 5). Given these ®ndings, it is unclear why lower inorganic arsenic concentrations were reported for seafood, meat and poultry in the present study compared to
844
R. A. Schoof et al. Table 3. Mean concentrations of total and inorganic arsenic in food Total arsenic (ng/g wet weight)
Inorganic arsenic (ng/g wet weight)
mean
(se)
Fats, oils, sweets Beet sugar Cane sugar Corn syrup Butter Soybean oil Salt Beer
12.2 23.8 6.0 1.8 U 1.5 J 4.8 2.7 J
(1.3) (2.7) (2.2) (0) (0.32) (3.0) (1.1)
3.5 4.4 0.4 1.1 0.8 0.8 1.8
Milk, yogurt, cheese Milk, skim (non-fat) Milk, whole
2.6 J 1.8 J
(1.2) (0.047)
1U 1U
(0) (0)
Meat, poultry, ®sh, eggs, nuts Beef Chicken Pork Eggs Saltwater ®n®sh Tuna Freshwater ®n®sh Shrimp Peanut butter
51.5 86.4 13.5 19.9 2,360 512 160 1,890 43.6
(11) (5.6) (0.99) (1.5) (1,311) (131) (132) (566) (21)
0.4 J 0.9 J 0.6 J 1J 0.5 J 1U 1J 1.9 J 4.7
(0.23) (0.10) (0.025) (0.27) (0.20) (0) (0.33) (0.26) (1.2)
Vegetables Beans (green) Carrots Corn (kernel) Cucumber Lettuce Onions Peas Potatoes Spinach Tomato
2.1 7.3 1.6 9.6 1.4 9.6 4.3 2.8 5.1 9.9
(0.26) (2.5) (0.12) (1.4) (0.25) (1.9) (1.1) (0.62) (1.8) (2.6)
1.2 3.9 1.1 4.1 1.5 3.3 4.5 0.8 6.1 0.9
J
(0.19) (1.4) (0.20) (1.2) (0.13) (0.74) (2.1) (0.36) (1.4) (0.35)
Fruit Apple, raw Apple, juice Banana Grapes Grape juice Orange Orange juice Peaches Watermelon
4.8 7.6 2.3 J 10.2 58.3 1.6 J 4.8 3.4 J 40.2
(3.1) (2.3) (0.74) (3.1) (3.0) (1.0) (1.3) (1.2) (2.8)
1.8 J 2.8 0.6 J 3.6 9.2 2.4 1U 2.3 8.9
(1.3) (0.44) (0.14) (1.2) (1.7) (0.83) (0) (0.26) (0.52)
Bread Corn (meal) Flour Rice
38.6 39.1 303
(6.1) (6.0) (61)
4.4 10.9 73.7
(0.90) (2.6) (9.6)
Water Tap water
1.8 U
(0)
0.8 J
(0.18)
J J J J
mean
J J J J J
J J J J
(se) (0.25) (1.1) (0.11) (0.22) (0.20) (0.27) (1.2)
Note: Mean values are the average of four samplesÐthree individual sample values and the average of the replicate samples of the fourth individual sample. All mean values were computed as follows: One-half the method detection limit was used for all ``U'' quali®ed values. If all values to be averaged were ``U '' quali®ed, the mean value was also ``U '' quali®ed. If the mean value was equivalent to or less than the method detection limit, a ``J '' quali®er was assigned. J-value reported is above blank concentration but less than the method detection limit se-standard error U-not detected; value reported is one-half of the method detection limit.
earlier studies. Buchet et al. (1994) also used HCl digestion and hydride AA analysis, while Mohri et al. (1990) used an alkaline (NaOH) digestion prior to hydride AA analysis. As in the present study, ®sh samples were collected at markets in the country in which the study was conducted. Additional studies will be necessary to con®rm the observed dierences in inorganic arsenic concentrations reported in studies of seafood from dierent countries.
The results of the present study con®rm that rice has higher inorganic arsenic concentrations than most other foods. Consequently, diets that rely heavily on rice may contain the most inorganic arsenic. In addition to rice, the data presented suggest that grains and produce are likely to be signi®cant contributors to dietary inorganic arsenic intake. Food consumption data will be combined with inorganic arsenic concentrations to explore the variation in arsenic intake within the United States
Survey of inorganic arsenic in food
845
Table 4. Arsenic concentrations in individual samples of selected foods (ng/g wet weight) Sample
Total arsenic
Inorganic arsenic
MMA
DMA
Saltwater ®n®sh Orange roughy CodÐsample 1 CodÐsample 2 Halibut Mean
568 6080 2320 466 2360
1U 0.3 J 0.1 J 0.7J 0.5 J
0.5 0.5 0.5 0.5 0.5
U U U U U
1J 5 4J 0.7 J 3
Canned tuna Sample 1 Sample 2 Sample 3 Sample 4 Mean
770 156 500 621 512
1 1 1 1 1
U U U U U
0.5 0.5 0.5 0.5 0.5
U U U U U
1J 6 3 2J 3
Shrimp Sample Sample Sample Sample Mean
1490 2790 473 2820 1890
2J 2 1J 3 1.9 J
0.5 0.5 0.5 0.5 0.5
U U U U U
29 57 21 31 34
Freshwater ®n®sh Cat®shÐsample 1 Cat®shÐsample 2 Cat®shÐsample 3 Rainbow Trout Mean
25 31 29 555 160
2J 1U 0.2 J 1U 1J
0.5 0.5 0.5 0.5 0.5
U U U U U
1 1 1 4 2
Raw rice Sample Sample Sample Sample Mean
335 218 462 196 303
55 62 81 97 73.7
0.5 U 0.5 U 3 3 2
1 2 3 4
1 2 3 4
U U U J
1U 61 202 99 91
Note: The fourth sample listed for all of the above foods is a mean of triplicate analyses for that sample. JÐestimates value observed above the blank concentration, but less than the method detection limit UÐnot detected at method detection limit; one-half the detection limit shown.
in a subsequent article. However, typical inorganic arsenic intakes are not expected to exceed those reported previously (i.e. 8±14 mg/day for adults) (Yost et al., 1998). Although this study relies on one sampling event in one state, the commodities sampled originated from diverse geographic locations (Table 1). This diversity re¯ects the homogeneous nature of contemporary US food supplies. Most of the foods with the highest inorganic arsenic concentrations were processed foods that would not be expected to have a local origin (i.e. rice, grape juice, cooked spinach, peanut butter, peas, cane sugar, corn meal and beet sugar). Seasonal in¯uences are also likely to be minimal in foods such as these that may be
stored for long periods without loss of quality. Consequently, the inorganic arsenic concentrations from this market basket survey are likely to be generally representative of typical concentrations in foods throughout the US. Arsenic may serve an essential role in growth and nutrition (Uthus, 1994a,b; Uthus and Seaborn, 1996). Based on studies of arsenic deprivation in laboratory animals, an arsenic requirement for humans eating 2000 kcal/day has been estimated to be in the range of 12 to 25 mg/day (Uthus, 1994b). De®ciencies related to low arsenic intakes would be most likely to appear in individuals with altered arsenic homeostasis or metabolic stress (Uthus, 1994a). These doses should be compared to toxic
Table 5. Comparison of arsenic concentrations in rice (uncooked) (ng/g wet weight) Source United Statesa (N = 4) Taiwanb (N = 5) Taiwanc (N = 5) Canadad (N = 1) a
Total arsenic
Inorganic arsenic
DMA
MMA
303
74
91
2
120
83
21
21
150
110
13
13
240
100
±
±
Present study (HCl digestion, hydride AA). Schoof et al. (1998) (HCl digestion, hydride AA). Schoof et al. (1998) (Split samples, ground, extracted with water and analysed by ICP-MS). d Yost et al. (1998) (HCl/HBr digestion, hydride AA), ``organic'' arsenic reported to be 160 ng/g. b c
846
R. A. Schoof et al.
doses of arsenic. While chronic daily inorganic arsenic intakes of 600 mg or more have been associated with adverse eects, the nature of the dose±response at lower doses is a subject of great debate (Chappell et al., 1997). Thus, accurate estimates of the range of arsenic dietary intakes and background exposures from other sources will be needed to balance nutritional needs with the possibility that suciently elevated concentrations in drinking water or in the environment might pose a threat to public health. AcknowledgementsÐThe authors would like to thank the following individuals for their assistance with this study: Darin Waylett of TAS-ENVIRON for assistance with study design and sample collection; Chuck Apts, Linda Bingler and Peg O'Neill of Battelle Marine Sciences for chemical analyses; Allyson Templeton of Exponent for spreadsheets and calculations; Laura Jones of Exponent for review of analytical methods; Matt Butcher of Exponent for statistical analyses; and Professor M. B. Dillencourt, L. Bic and Edward Lee of the University of California at Irvine for preliminary designs and excellent constructive criticism.
REFERENCES
Beauchemin D., Bednas M. E., Berman S. S., McLaren J. W., Siu K. W. M. and Sturgeon R. E. (1988) Identi®cation and quantitation of arsenic species in a dog®sh muscle reference material for trace elements. Analytical Chemistry 60, 2209±2212. Buchet J. P., Lison D., Ruggeri M., Foa V. and Elia G. (1996) Assessment of exposure to inorganic arsenic, a human carcinogen, due to the consumption of seafood. Archives of Toxicology 70, 773±778. Buchet J. P., Pauwels J. and Lauwerys R. (1994) Assessment of exposure to inorganic arsenic following ingestion of marine organisms by volunteers. Environmental Research 66, 44±51. Chappell W. R., Beck B. D., Brown K. G., Chaney R., Cothern C. R., Irgolic K. J., North D. W., Thornton I. and Tsongas T. A. (1997) Inorganic arsenic: a need and an opportunity to improve risk assessment. Environmental Health Perspectives 105, 1060±1067. Dabeka R. W., McKenzie A. D., Lacroix G. M. A., Cleroux C., Bowe S., Graham R. A., Conacher H. B. S. and Verdier P. (1993) Survey of arsenic in total diet food composites and estimation of the dietary intake of arsenic by Canadian adults and children. Journal of AOAC International 76, 14±25. FDA (1997) Total arsenic data from an electronic database consisting of all results from total diet study market baskets collected from 1986 to 1994. Dataset. US Food and Drug Administration, Washington, DC. Francesconi K. A. and Edmonds J. S. (1994) Biotransformation of arsenic in the marine environment. In Arsenic in the Environment, Part I: Cycling and Characterization, ed. J. O. Nriagu, pp. 221±263. John Wiley & Sons, New York. Gunderson E. L. (1995) FDA total diet study, July 1986± April 1991, dietary intakes of pesticides, selected elements, and other chemicals. Journal of AOAC International 78, 1353±1363. Jelinek C. F. and Corneliussen P. E. (1977) Levels of arsenic in the United States food supply. Environmental Health Perspectives 19, 83±87. Mohri T., Hisanaga A. and Ishinishi N. (1990) Arsenic intake and excretion by Japanese adults: a 7-day dupli-
cate diet study. Food and Chemical Toxicology 28, 521± 529. Pennington and Jean A. T. (1992) Appendix BÐ Preparation and Cooking Instructions for Total Diet Study Foods, From Appendices for the 1990 Revision of the Food and Drug Administration's Total Diet Food List and Diets. Center for Food Safety and Applied Nutrition (CFSAN), US Food and Drug Administration (FDA). NTIS # PB92-176239. Phillips D. J. H. (1994) The chemical forms of arsenic in aquatic organisms and their interrelationships. In Arsenic in the Environment, Part I: Cycling and Characterization, ed. J. O. Nriagu, pp. 263±288. John Wiley & Sons, New York. Schoof R. A., Yost L. J., Crecelius E., Irgolic K., Goessler W., Guo H.-R. and Greene H. L. (1998) Dietary arsenic intake in Taiwanese districts with elevated arsenic in drinking water. Human and Ecological Risk Assessment 4, 117±135. Schroeder H. A. and Balassa J. J. (1966) Abnormal trace metals in man: arsenic. Journal of Chronic Disease 19, 85±106. Shiomi K. (1994) Arsenic in marine organisms: chemical forms and toxicological aspects. In Arsenic in the Environment, Part II: Human Health and Ecosystem Eects, ed. J. O. Nriagu, pp. 261±282. John Wiley & Sons, New York. Tsuda T., Inoue T., Kojima M. and Shigeru A. (1995) Market basket and duplicate portion estimation of dietary intakes of cadmium, mercury, arsenic, copper, manganese, and zinc by Japanese adults. Journal of AOAC International 78, 1363±1368. Uthus E. O. (1994a) Arsenic essentiality studies and factors aecting its importance. In Arsenic Exposure and Health, ed. W. R. Chappell, C. O. Abernathy and C. R. Cothern, pp. 199±208. Science and Technology Letters, Northwood, UK. Uthus E. O. (1994b) Estimation of safe and adequate daily intake for arsenic. In Risk Assessment of Essential Elements, ed. W. Mertz, C. O. Abernathy and S. S. Olin, pp. 273±282. ILSI Press, Washington, DC. Uthus E. O. and Seaborn C. D. (1996) RDA Workshop: New approaches, endpoints and paradigms for RDAs for mineral elements. Journal of Nutrition 126 (Suppl. Sep. 1996), S2452±S2459. USDA (1992) Nationwide Food Consumption Survey: Continuing Survey of Food Intakes by Individuals 1989±90. Dataset. US Department of Agriculture, Human Nutrition Information Service, Washington, DC. USDA (1993) Nationwide Food Consumption Survey: Continuing Survey of Food Intakes by Individuals 1990±91. Dataset. US Department of Agriculture, Human Nutrition Information Service, Washington, DC. USDA (1994) Nationwide Food Consumption Survey: Continuing Survey of Food Intakes by Individuals 1991±92. Dataset. US Department of Agriculture, Human Nutrition Information Service, Washington, DC. US EPA (1996) Method 1632, inorganic arsenic in water by hydride generation quartz furnace atomic absorption. EPA/821/R-95/028. US Environmental Protection Agency, Oce of Water, Oce of Science and Technology, Engineering and Analysis Division, Washington, DC. Yamauchi H. and Fowler B. A. (1994) Toxicity and metabolism of inorganic and methylated arsenicals. In Arsenic in the Environment, Part II: Human Health and Ecosystem Eects, ed. J. O. Nriagu, pp. 35±54. John Wiley & Sons, New York.
www.elsevier.com/locate/foodchemtox
Research Section
A Market Basket Survey of Inorganic Arsenic in Food R. A. SCHOOF1*, L. J. YOST1, J. EICKHOFF2, E. A. CRECELIUS3, D. W. CRAGIN4, D. M. MEACHER5 and D. B. MENZEL5 Exponent, Bellevue, WA, 2ENVIRON, Arlington, VA, 3Battelle Marine Sciences, Sequim, WA, 4Elf Atochem North America, Inc., Philadelphia, PA and 5University of California, Irvine, CA, USA
1
(Accepted 7 February 1999) AbstractÐDietary arsenic intake estimates based on surveys of total arsenic concentrations appear to be dominated by intake of the relatively non-toxic, organic arsenic forms found in seafood. Concentrations of inorganic arsenic in food have not been not well characterized. Accurate dietary intake estimates for inorganic arsenic are needed to support studies of arsenic's status as an essential nutrient, and to establish background levels of exposure to inorganic arsenic. In the market basket survey reported here, 40 commodities anticipated to provide at least 90% of dietary inorganic arsenic intake were identi®ed. Four samples of each commodity were collected. Total arsenic was analysed using an NaOH digestion and inductively coupled plasma±mass spectrometry. Separate aliquots were analysed for arsenic species using an HCl digestion and hydride atomic absorption spectroscopy. Consistent with earlier studies, total arsenic concentrations (all concentrations reported as elemental arsenic per tissue wet weight) were highest in the seafoods sampled (ranging from 160 ng/g in freshwater ®sh to 2360 ng/ g in saltwater ®sh). In contrast, average inorganic arsenic in seafood ranged from less than 1 ng/g to 2 ng/g. The highest inorganic arsenic values were found in raw rice (74 ng/g), followed by ¯our (11 ng/g), grape juice (9 ng/g) and cooked spinach (6 ng/g). Thus, grains and produce are expected to be signi®cant contributors to dietary inorganic arsenic intake. # 1999 Elsevier Science Ltd. All rights reserved Keywords: inorganic arsenic; dietary exposures; arsenic in food. Abbreviations: DMA = dimethylarsenic acid; MMA = monomethylarsonic acid.
INTRODUCTION
Arsenic has been detected in most foods tested. Although arsenic may be present in foods in a variety of organic compounds as well as in inorganic forms, most studies have reported only total arsenic concentrations. Based on studies in laboratory animals, inorganic arsenic may be a required nutrient for humans; however, the required intakes and the intakes from typical diets are not well characterized (Uthus, 1994a,b; Uthus and Seaborn, 1996). During the last two decades, much progress has been made in understanding the forms and concentrations of arsenic in some foods. The primary focus of prior research has been on arsenic in aquatic organisms, many of which contain total arsenic concentrations two to three orders of magnitude greater than total arsenic concentrations in foods of terrestrial origin *Corresponding author.
(Jelinek and Corneliussen, 1977; Schroeder and Balassa, 1966). Studies of the arsenic forms found in ®n®sh and shell®sh have demonstrated that most arsenic in these foods occurs as methylated arsenic compounds, with only small amounts of inorganic arsenic present (Buchet et al., 1994; Francesconi and Edmonds, 1994; Phillips, 1994; Yost et al., 1998). Inorganic arsenic is not formed after ingestion of these compounds (Buchet et al., 1994, 1996), indicating little or no metabolism in humans to the most toxic forms of arsenic. The complex arsenic compounds that predominate in marine organisms are much less acutely toxic than soluble inorganic arsenic compounds, with arsenobetaine (the predominant compound in ®n®sh) being virtually nontoxic (Shiomi, 1994; Yamauchi and Fowler, 1994). Monomethylarsonic (MMA) and dimethylarsenic (DMA) acids are also less acutely toxic than the
0278-6915/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. Printed in Great Britain PII S0278-6915(99)00073-3
840
R. A. Schoof et al.
inorganic forms, arsenite (As3+) and arsenate (As5+). The forms of arsenic present in foods of terrestrial origin are not well characterized, largely due to their occurrence at ng/g concentrations that are below the detection limits of many analytical methods. In contrast, the methylated arsenic forms in seafood, which occur at mg/g concentrations, have been much more thoroughly studied (Francesconi and Edmonds, 1994). Methylated arsenic compounds are much less prevalent in terrestrial food sources than in seafood. A recent report indicates that between 25 and 100% of total arsenic in terrestrial foods may be inorganic arsenic (Yost et al., 1998). Accurate estimates of the forms of arsenic in the diet are an important component of evaluations of background arsenic exposures and of possible nutritional status for this microelement. However, most dietary studies have reported only total arsenic concentrations. For example, recent diet studies that included evaluations of total arsenic in foods have been reported for Canada, the United States, and Japan (Dabeka et al., 1993; Gunderson, 1995; Tsuda et al., 1995). These studies used market basket survey techniques in which a large number of foods or food composites were tested, often after cooking, for total arsenic concentrations. Food consumption data were then used to estimate daily arsenic intakes. Daily intake estimates varied substantially among the three countries, from 38.6 mg total arsenic for young American men to 59.2 mg for a similar age group of Canadian men, with far higher values being reported for Japanese women (160 and 280 mg during two dierent years) (Dabeka et al., 1993; Gunderson, 1995; Tsuda et al., 1995). In all three countries, total arsenic intake was dominated by arsenic from seafood. Thus, the variations in daily arsenic intake among residents of dierent countries largely re¯ect variations in seafood consumption. Seafood accounted for almost 90% of daily arsenic intake in the United States (Gunderson, 1995), approximately 70% in Canada (Dabeka et al., 1993), and 60±70% in Japan (Tsuda et al., 1995). In Japan, an additional factor was consumption of seaweed and rice, which accounted for most of the remaining arsenic intake. Some indirect estimates of inorganic arsenic intakes can be made from the studies of total arsenic in the diet if seafood sources of arsenic are excluded (based on the assumption that almost all arsenic in seafood is organic, while arsenic in terrestrial foods is mostly inorganic). For example, in young American men, only 4.5 mg of daily arsenic intake was attributable to sources other than seafood (Gunderson, 1995). In young Canadian men, approximately 20 mg arsenic per day was from nonseafood sources (Dabeka et al., 1993).
Direct measurements of inorganic arsenic in diets are scanty. A duplicate diet study of Japanese adults reported an average daily inorganic arsenic intake of 13.7 mg when total arsenic intake was 202 mg (Mohri et al., 1990). A recent study suggests that typical North American diets contain less than 15 mg inorganic arsenic per day, but these estimates are considered preliminary due to the limited number of foods for which inorganic arsenic concentrations were available (Yost et al., 1998). The study reported here provides inorganic arsenic concentrations for a wide variety of foods, selected so that a market basket approach can be used to estimate inorganic arsenic intake from the diet.
MATERIALS AND METHODS
Market basket design and sample collection Food consumption data from the US Department of Agriculture Continuing Surveys of Food Intakes by Individuals (USDA, 1992, 1993, 1994), surveys of total arsenic in food (Dabeka et al., 1993; FDA, 1997), and estimates of inorganic arsenic concentrations in food (Yost et al., 1998) were used to select 40 commodities that were predicted to account for at least 90% of the dietary inorganic arsenic in the United States. The USDA consumption data were used to determine the foods consumed in the largest quantities. Total arsenic levels in foods from the total diet studies conducted in the United States and Canada were adjusted to re¯ect predicted inorganic arsenic levels and used to identify foods likely to have the highest inorganic arsenic levels. All foods thus identi®ed (high consumption and/or expected high levels of inorganic arsenic) were included in inorganic arsenic dietary intake analyses for the United States. The estimated intakes for the foods (consumption inorganic arsenic concentration) were ordered from highest to lowest; the foods that together contributed the top 90% of inorganic arsenic intake were selected for the market basket survey. A modi®ed market basket survey method was used to collect four samples of each commodity. The food samples were collected during October 1997 from large supermarkets in two towns in Texas, two samples each from Bryan and Tyler (except that the ``Tyler'' beer samples were collected in Coee City, Texas). Tap water was also included in the study; samples were collected in a hotel (Tyler samples) and in restaurants (Bryan samples). The food samples were prepared in accordance with Appendix B from Appendices for the 1990 Revision of the Food and Drug Administration's Total Diet Food List and Diets (Pennington, 1992), with some exceptions. Rice samples were not cooked (raw rice was tested to facilitate comparisons with arsenic concentrations reported in previous studies). Vegetables were cooked in a
Survey of inorganic arsenic in food
microwave oven, instead of being boiled in water. Commodities collected, a description of the samples, the state or country of origin of the raw commodity (if known), and a brief description of the preparation/cooking methods are presented in Table 1. Each sample was then analysed separately (i.e. no composites were prepared). Sample analyses All samples were analysed at Battelle Marine Sciences in Sequim, Washington. Total arsenic was analysed in food commodities after NaOH digestion by inductively coupled plasma±mass spectrometry (ICP±MS). Approximately one in every 10 samples was analysed in triplicate. For the digestion of liquids (milk, juices and water), NaOH was added to 8 g liquid to produce 2 N NaOH solution. This solution was heated for 16 hr at 808C. For the digestion of solid food, either 1 or 2 g food was digested in 13 ml 2 N NaOH for 16 hr at 808C. In preparation for ICP±MS analysis, 1 ml digestate was diluted with 9 ml 2% concentrated HNO3. A model Elan 5000 Perkin-Elmer ICP±MS was operated using the stock cross-¯ow nebulizer. Several ions were monitored to evaluate polyatomic interference from Ar40 Cl35, which has the same mass as arsenic. When interference occurred, the manufacturer's correction factor was used to reduce the interference. Food samples were digested for analysis of total arsenic using NaOH instead of HNO3, which had been used in a previous study of arsenic in rice and yams (Schoof et al., 1998). The NaOH digestion was expected to be more eective than HNO3 in dissolving food with high fat content. A comparison between these two types of digestions on ®ve dierent rice samples resulted in a relative percent dierence of 10% between the mean concentrations. Total arsenic results for oyster tissue digested with NaOH or HNO3 agreed within 5%. Analysis of standard reference bovine liver (certi®ed 0.055 mg/g As) digested with NaOH resulted in 0.071 mg/g and digested with HNO3 resulted in 0.062 mg/g. These results indicate that both digestion methods are comparable and accurate. Arsenic speciation was determined in food samples digested with HCl. Between 0.5 and 2 g of food was digested with 13 ml 2 N HCl at 808C for 16 hr. The digestates were stored at 48C before analysis by EPA Method 1632, (US EPA, 1996). A 2-ml aliquot of the digestate was analysed for As3+ by arsine generation at pH 6 with the reducing agent sodium borohydride. The hydride was collected on a cryogenic column before quanti®cation by atomic absorption (AA) using a quartz tube with an air±hydrogen ¯ame positioned in the light path. The HCl digestion is eective in dissolving the arsenic compounds in food without changing the oxidative states of As3+ and As5+ (Beauchemin
841
et al., 1988; Schoof et al., 1998). Also, MMA and DMA are not decomposed during the digestion. Recovery of matrix spikes of As3+, As5+, MMA and DMA added to 21 dierent foods indicates that the digestion process does not alter the speciation of these four compounds. Mean spike recoveries for the four arsenic species were 92% for As3+, 86% for As5+, 89% for MMA and 98% for DMA. Because there are few published data on arsenic speciation in food, comparisons with other digestion methods are limited. The Canadian National Research Council reported the certi®ed reference material DORM-1 (dog®sh muscle) contained 0.472 0.02 mg/g DMA (Beauchemin et al., 1988). Our results for seven replicates of DORM-1, analysed with dierent batches of food, had a mean and standard deviation of 0.56 2 0.07 mg/g. The concentrations of arsenic species were stable for over 1 month in the digestates of certi®ed reference materials stored at 48C. The quanti®cation of total inorganic arsenic, MMA and DMA was conducted similarly to that of As3+, except that arsines were generated at pH 1. The three arsines (arsine, methylarsine and dimethylarsine) were collected on the cold column, then quanti®ed by AA when the column was heated. The dierent column retention times of the arsines allows quanti®cation of inorganic arsenic, MMA and DMA. The concentration of As5+ is determined by the dierence between inorganic arsenic and As3+. Every fourth sample was analysed in triplicate. The data were blank-corrected by subtracting the mean of the procedural blanks. The mean blank concentrations are shown in Table 2. The method detection limits were determined from the variance in triplicate analyses of food samples containing low but detectable arsenic. The standard deviation was multiplied by the Student's t-value for 95% con®dence level. The method detection limits are shown in Table 2. If no arsenic was detected (after blank correcting), one-half the value of the method detection limit was given with a ``U '' ¯ag. One-half the detection limit was used in subsequent calculations. Mean values have a ``U '' quali®er if all values used to calculate the mean were ``U '' quali®ed. When the concentration of arsenic in food (after blank correcting) was detected above the blank concentration but below the method detection limit, the value was ``J'' ¯agged. The same rule as was used for the ``U'' ¯agged values was also applied in assigning ``J'' quali®ers to mean values. RESULTS
Table 3 shows mean concentrations of total and inorganic arsenic for 40 commodities and tap water. The data from the two towns from which food samples were collected did not dier signi®cantly.
842
R. A. Schoof et al. Table 1. Commodities tested: description and preparation method
Food Fats, oils, sweets Sugar (beet) Sugar (cane) Corn syrup Butter Soybean oil Salt Beer Milk, yogurt, cheese Milk, skim Milk, whole Meat, poultry, ®sh, eggs, nuts Beef Chicken Pork Eggs Saltwater ®n®sh Tuna Freshwater ®n®sh Shrimp Peanut butter Vegetables Beans (green) Carrots Corn (kernel) Cucumber Lettuce Onions Peas Potatoes Spinach Tomato Fruit Apple, raw Apple, juice Banana Grapes Grape juice Orange Orange juice Peaches Watermelon Bread, cereal, rice, pasta Corn (meal) Flour (wheat) Rice Water Tap water 1
Sample description (origin)1
Preparation method
Granulated sugar (unknown) Granulated sugar (unknown) Light corn syrup (unknown) Unsalted sweet cream butter (1 Illinois, 2 Minnesota, 1 Ohio) Soybean/vegetable oil (unknown) Iodized salt (unknown) Bottled beer (2 Texas, 2 Missouri)
As As As As
Vitamin A & D skim milk (1 Ohio, 1 Texas, 2 Utah) Vitamin D whole milk (1 Ohio, 1 Texas, 2 Utah)
As is
Top sirloin steak (1 Texas, 3 unknown) Split chicken breasts with rib (1 Georgia, 1 Texas, 2 unknown) Pork loin chops (2 Minnesota, 1 Ohio, 1 Texas) Large, grade A eggs (2 Texas, 2 unknown) Orange roughy ®llet [1], cod ®llet [2], halibut steak [1] (unknown) Chunk light tuna packed in water (unknown) Cat®sh ®llet [3], rainbow trout [1] (1 Texas, 2 unknown, 1 Idaho) Shrimp (1 Gulf of Mexico, 1 Mexico, 2 unknown) Creamy peanut butter (unknown) Cut/frozen green beans (1 Wisconsin, 1 Minnesota, 1 unknown, 1 Tennessee) Bagged/loose carrots (2 Colorado, 1 California, 1 unknown) Cut/frozen whole kernel corn (1 Ohio, 2 Wisconsin, 1 unknown) Cucumber (unknown) Iceberg head lettuce/salad (4 California) Yellow/white onions(2 Colorado, 2 unknown) Frozen peas (1 Minnesota, 2 Wisconsin, 1 unknown) Russet/Idaho/long potatoes (1 California, 1 Idaho, 1 Washington, 1 unknown) Frozen chopped/cut leaf spinach (2 Georgia, 1 Wisconsin, 1 unknown) Roma/vine-ripened tomatoes (3 California, 1 Mexico) Red delicious/Jonathon/McIntosh apples (2 Washington, 1 Michigan, 1 Missouri) Apple juice (1 US, 1 Washington, 1 Hungary, 1 unknown) Banana (4 Guatemala) Red/green Thompson seedless grapes (3 California, 1 Nicaragua) Grape juice (2 US, 2 unknown) Navel/Valencia oranges (1 New Mexico, 2 Texas, 1 Australia) Frozen concentrated orange juice (4 US/Brazil mixture) Peaches from mixed fruit/frozen peaches (unknown) Cut watermelon/seedless/fresh watermelon (1 New Mexico, 1 Mexico, 2 unknown)
is is is is
As is As is As is
As is
Baked 30 min at 3508F Baked (with skin) until done at 3508F Baked 30 min at 3508F Peeled, boiled 3 min Baked 15±25 min at 3508±4008F Drained Baked (bones removed) until done microwaved (shelled) As is Microwaved 6±12 min (no water added) Peeled, microwaved 4±8 min (ends removed) Microwaved 6±7 min (no water added) Peeled (ends removed) Washed (individual leaves), drained Peeled (®rst layer removed) Microwaved 4±6 min (no water added) Peeled, some chopped, microwaved 10 min or until tender Microwaved 4±6 min Washed (skin left on)
Washed, peeled, cored (skin left on) As is (single strength) Peeled Washed in cool water, stems removed As is (single strength) Peeled, excess white membrane and seeds removed As is (concentrated) As is Rind and most seeds removed
Enriched/stone-ground/all-purpose/degerminated corn meal (2 unknown, 2 Texas) Graham/whole wheat ¯our (unknown- US) Long grain enriched rice (1 unknown, 3 Texas)
As is
Local taps/drink dispenser
As is (ran tap for 2 min)
The state or country where the raw commodity was produced is listed when known
As is As is (uncooked)
Survey of inorganic arsenic in food Table 2. Mean blank concentrations and method detection limits (ng/g wet weight)
Astot Asi As+3 As+5 MMA DMA
Mean blank concentrations
Method detection limits
4.57 1.96 <1 1.96 <1 <2
3.6 2 1 2 1 2
Note: Astot-total arsenic Asi-inorganic arsenic MMA-monomethylarsonic acid DMA-dimethylarsinic acid.
Consequently, the data for all four samples of each commodity were averaged. Total arsenic was detected in two or more samples of 35 of the 40 commodities, that is, all of the commodities except butter, soybean/vegetable oil, salt, whole milk and green beans. Inorganic arsenic was detected in two or more samples of 34 of the 40 commodities, that is, all commodities except soybean/vegetable oil, whole and skim milk, chicken, tuna and orange juice. Inorganic arsenic concentrations were either undetected or ``J`` quali®ed in approximately one-half of the samples, suggesting that the detection limits achieved in this study are just sucient to characterize inorganic arsenic concentrations in a wide variety of foods. Consistent with earlier studies, total arsenic concentrations (all concentrations reported as elemental arsenic per tissue wet weight) were highest in the four kinds of seafood sampled (means ranged from 160 ng/g in freshwater ®sh to 2360 ng/g in saltwater ®sh). In contrast, average inorganic arsenic mean concentrations in seafood ranged from less than 1 ng/g to 2 ng/g. Marked variation in total arsenic concentrations observed in ®n®sh samples may re¯ect variations among species (Table 4). Concentrations were more consistent among canned tuna samples. The next highest total arsenic concentrations occurred in rice (303 ng/g), which also had the highest concentrations of inorganic arsenic (Table 3). Other foods with relatively high (i.e. greater than 10 ng/g) total arsenic concentrations included foods high in protein (i.e. beef, chicken, pork, eggs and peanut butter) or sugar (i.e. beet sugar, cane sugar, grapes and grape juice), and grains (i.e. corn meal and ¯our). The inorganic arsenic concentrations in raw rice (74 ng/g) were much higher than concentrations in other foods. The next highest concentrations of inorganic arsenic were in ¯our (11 ng/g), grape juice (9 ng/g), cooked spinach (6 ng/g), peanut butter (5 ng/g), peas (5 ng/g), as well as cane sugar, corn meal, cucumber and beet sugar (all 4 ng/g). Inorganic arsenic concentrations were low enough in most foods that it was not clear what arsenic forms predominated (i.e. As3+ or As5+); however,
843
in rice, ¯our, grape juice, spinach, peanut butter and cucumber, the concentrations of As3+ were generally more than twice the concentration of As5+. In contrast, cane sugar and beet sugar appeared to have more As5+ than As3+ (data not shown). In fruits and vegetables, inorganic arsenic accounted for approximately one-half of the total arsenic (Table 3). In grains, sugars and oil, inorganic arsenic accounted for approximately onequarter of the total arsenic, while only a small fraction of the total was inorganic in meat, poultry, ®sh and eggs. With a few exceptions, both MMA and DMA concentrations were undetected or very low. Rice and shell®sh (shrimp) were the commodities with the highest DMA concentrations, with mean concentrations of 91 and 34 ng/g, respectively (Table 4). The next highest concentrations of DMA were in beet sugar and cane sugar, with concentrations of 7 and 8 ng/g, respectively (data not shown). DMA was also detected at low concentrations in seafood (Table 4), meat and fruits and fruit juices (data not shown). MMA was repeatedly detected only in samples of apple juice (data not shown) and rice (Table 4). DISCUSSION
Inorganic arsenic was found at ng/g concentrations in most foods tested. Concentrations for inorganic arsenic reported in the present study were generally lower than those previously reported for seafood, meat and poultry, even though total arsenic concentrations were similar among studies. For example, while inorganic arsenic concentrations in saltwater ®n®sh (cod, halibut, orange roughy, canned tuna) were less than 1 ng/g in the present study, three previous studies reported values from 5 to 28 ng/g for similar ®sh species (Buchet et al., 1994, Mohri et al., 1990; Yost et al., 1998). Similarly, inorganic arsenic concentrations in shrimp ranged from 1 to 3 ng/g in the four samples tested in the present study, compared to values of 37 ng/g (Mohri et al., 1990) and 100 ng/g (Yost et al., 1998) in two samples tested previously. Meat and poultry products tested in the present study (N = 12) also contained 1 ng/g or less of inorganic arsenic, compared to 9 to 24 ng/g reported in a previous study (Yost et al., 1998). Inorganic arsenic concentrations in other foods were generally consistent with previously reported values. Inorganic arsenic concentrations have been notably consistent among rice samples tested by several methods, with average values ranging from 74 to 110 ng/g (Table 5). In particular, similar concentrations were reported for split samples analysed by hydride AA after HCl digestion or by ICP±MS after a water-based extraction (Table 5). Given these ®ndings, it is unclear why lower inorganic arsenic concentrations were reported for seafood, meat and poultry in the present study compared to
844
R. A. Schoof et al. Table 3. Mean concentrations of total and inorganic arsenic in food Total arsenic (ng/g wet weight)
Inorganic arsenic (ng/g wet weight)
mean
(se)
Fats, oils, sweets Beet sugar Cane sugar Corn syrup Butter Soybean oil Salt Beer
12.2 23.8 6.0 1.8 U 1.5 J 4.8 2.7 J
(1.3) (2.7) (2.2) (0) (0.32) (3.0) (1.1)
3.5 4.4 0.4 1.1 0.8 0.8 1.8
Milk, yogurt, cheese Milk, skim (non-fat) Milk, whole
2.6 J 1.8 J
(1.2) (0.047)
1U 1U
(0) (0)
Meat, poultry, ®sh, eggs, nuts Beef Chicken Pork Eggs Saltwater ®n®sh Tuna Freshwater ®n®sh Shrimp Peanut butter
51.5 86.4 13.5 19.9 2,360 512 160 1,890 43.6
(11) (5.6) (0.99) (1.5) (1,311) (131) (132) (566) (21)
0.4 J 0.9 J 0.6 J 1J 0.5 J 1U 1J 1.9 J 4.7
(0.23) (0.10) (0.025) (0.27) (0.20) (0) (0.33) (0.26) (1.2)
Vegetables Beans (green) Carrots Corn (kernel) Cucumber Lettuce Onions Peas Potatoes Spinach Tomato
2.1 7.3 1.6 9.6 1.4 9.6 4.3 2.8 5.1 9.9
(0.26) (2.5) (0.12) (1.4) (0.25) (1.9) (1.1) (0.62) (1.8) (2.6)
1.2 3.9 1.1 4.1 1.5 3.3 4.5 0.8 6.1 0.9
J
(0.19) (1.4) (0.20) (1.2) (0.13) (0.74) (2.1) (0.36) (1.4) (0.35)
Fruit Apple, raw Apple, juice Banana Grapes Grape juice Orange Orange juice Peaches Watermelon
4.8 7.6 2.3 J 10.2 58.3 1.6 J 4.8 3.4 J 40.2
(3.1) (2.3) (0.74) (3.1) (3.0) (1.0) (1.3) (1.2) (2.8)
1.8 J 2.8 0.6 J 3.6 9.2 2.4 1U 2.3 8.9
(1.3) (0.44) (0.14) (1.2) (1.7) (0.83) (0) (0.26) (0.52)
Bread Corn (meal) Flour Rice
38.6 39.1 303
(6.1) (6.0) (61)
4.4 10.9 73.7
(0.90) (2.6) (9.6)
Water Tap water
1.8 U
(0)
0.8 J
(0.18)
J J J J
mean
J J J J J
J J J J
(se) (0.25) (1.1) (0.11) (0.22) (0.20) (0.27) (1.2)
Note: Mean values are the average of four samplesÐthree individual sample values and the average of the replicate samples of the fourth individual sample. All mean values were computed as follows: One-half the method detection limit was used for all ``U'' quali®ed values. If all values to be averaged were ``U '' quali®ed, the mean value was also ``U '' quali®ed. If the mean value was equivalent to or less than the method detection limit, a ``J '' quali®er was assigned. J-value reported is above blank concentration but less than the method detection limit se-standard error U-not detected; value reported is one-half of the method detection limit.
earlier studies. Buchet et al. (1994) also used HCl digestion and hydride AA analysis, while Mohri et al. (1990) used an alkaline (NaOH) digestion prior to hydride AA analysis. As in the present study, ®sh samples were collected at markets in the country in which the study was conducted. Additional studies will be necessary to con®rm the observed dierences in inorganic arsenic concentrations reported in studies of seafood from dierent countries.
The results of the present study con®rm that rice has higher inorganic arsenic concentrations than most other foods. Consequently, diets that rely heavily on rice may contain the most inorganic arsenic. In addition to rice, the data presented suggest that grains and produce are likely to be signi®cant contributors to dietary inorganic arsenic intake. Food consumption data will be combined with inorganic arsenic concentrations to explore the variation in arsenic intake within the United States
Survey of inorganic arsenic in food
845
Table 4. Arsenic concentrations in individual samples of selected foods (ng/g wet weight) Sample
Total arsenic
Inorganic arsenic
MMA
DMA
Saltwater ®n®sh Orange roughy CodÐsample 1 CodÐsample 2 Halibut Mean
568 6080 2320 466 2360
1U 0.3 J 0.1 J 0.7J 0.5 J
0.5 0.5 0.5 0.5 0.5
U U U U U
1J 5 4J 0.7 J 3
Canned tuna Sample 1 Sample 2 Sample 3 Sample 4 Mean
770 156 500 621 512
1 1 1 1 1
U U U U U
0.5 0.5 0.5 0.5 0.5
U U U U U
1J 6 3 2J 3
Shrimp Sample Sample Sample Sample Mean
1490 2790 473 2820 1890
2J 2 1J 3 1.9 J
0.5 0.5 0.5 0.5 0.5
U U U U U
29 57 21 31 34
Freshwater ®n®sh Cat®shÐsample 1 Cat®shÐsample 2 Cat®shÐsample 3 Rainbow Trout Mean
25 31 29 555 160
2J 1U 0.2 J 1U 1J
0.5 0.5 0.5 0.5 0.5
U U U U U
1 1 1 4 2
Raw rice Sample Sample Sample Sample Mean
335 218 462 196 303
55 62 81 97 73.7
0.5 U 0.5 U 3 3 2
1 2 3 4
1 2 3 4
U U U J
1U 61 202 99 91
Note: The fourth sample listed for all of the above foods is a mean of triplicate analyses for that sample. JÐestimates value observed above the blank concentration, but less than the method detection limit UÐnot detected at method detection limit; one-half the detection limit shown.
in a subsequent article. However, typical inorganic arsenic intakes are not expected to exceed those reported previously (i.e. 8±14 mg/day for adults) (Yost et al., 1998). Although this study relies on one sampling event in one state, the commodities sampled originated from diverse geographic locations (Table 1). This diversity re¯ects the homogeneous nature of contemporary US food supplies. Most of the foods with the highest inorganic arsenic concentrations were processed foods that would not be expected to have a local origin (i.e. rice, grape juice, cooked spinach, peanut butter, peas, cane sugar, corn meal and beet sugar). Seasonal in¯uences are also likely to be minimal in foods such as these that may be
stored for long periods without loss of quality. Consequently, the inorganic arsenic concentrations from this market basket survey are likely to be generally representative of typical concentrations in foods throughout the US. Arsenic may serve an essential role in growth and nutrition (Uthus, 1994a,b; Uthus and Seaborn, 1996). Based on studies of arsenic deprivation in laboratory animals, an arsenic requirement for humans eating 2000 kcal/day has been estimated to be in the range of 12 to 25 mg/day (Uthus, 1994b). De®ciencies related to low arsenic intakes would be most likely to appear in individuals with altered arsenic homeostasis or metabolic stress (Uthus, 1994a). These doses should be compared to toxic
Table 5. Comparison of arsenic concentrations in rice (uncooked) (ng/g wet weight) Source United Statesa (N = 4) Taiwanb (N = 5) Taiwanc (N = 5) Canadad (N = 1) a
Total arsenic
Inorganic arsenic
DMA
MMA
303
74
91
2
120
83
21
21
150
110
13
13
240
100
±
±
Present study (HCl digestion, hydride AA). Schoof et al. (1998) (HCl digestion, hydride AA). Schoof et al. (1998) (Split samples, ground, extracted with water and analysed by ICP-MS). d Yost et al. (1998) (HCl/HBr digestion, hydride AA), ``organic'' arsenic reported to be 160 ng/g. b c
846
R. A. Schoof et al.
doses of arsenic. While chronic daily inorganic arsenic intakes of 600 mg or more have been associated with adverse eects, the nature of the dose±response at lower doses is a subject of great debate (Chappell et al., 1997). Thus, accurate estimates of the range of arsenic dietary intakes and background exposures from other sources will be needed to balance nutritional needs with the possibility that suciently elevated concentrations in drinking water or in the environment might pose a threat to public health. AcknowledgementsÐThe authors would like to thank the following individuals for their assistance with this study: Darin Waylett of TAS-ENVIRON for assistance with study design and sample collection; Chuck Apts, Linda Bingler and Peg O'Neill of Battelle Marine Sciences for chemical analyses; Allyson Templeton of Exponent for spreadsheets and calculations; Laura Jones of Exponent for review of analytical methods; Matt Butcher of Exponent for statistical analyses; and Professor M. B. Dillencourt, L. Bic and Edward Lee of the University of California at Irvine for preliminary designs and excellent constructive criticism.
REFERENCES
Beauchemin D., Bednas M. E., Berman S. S., McLaren J. W., Siu K. W. M. and Sturgeon R. E. (1988) Identi®cation and quantitation of arsenic species in a dog®sh muscle reference material for trace elements. Analytical Chemistry 60, 2209±2212. Buchet J. P., Lison D., Ruggeri M., Foa V. and Elia G. (1996) Assessment of exposure to inorganic arsenic, a human carcinogen, due to the consumption of seafood. Archives of Toxicology 70, 773±778. Buchet J. P., Pauwels J. and Lauwerys R. (1994) Assessment of exposure to inorganic arsenic following ingestion of marine organisms by volunteers. Environmental Research 66, 44±51. Chappell W. R., Beck B. D., Brown K. G., Chaney R., Cothern C. R., Irgolic K. J., North D. W., Thornton I. and Tsongas T. A. (1997) Inorganic arsenic: a need and an opportunity to improve risk assessment. Environmental Health Perspectives 105, 1060±1067. Dabeka R. W., McKenzie A. D., Lacroix G. M. A., Cleroux C., Bowe S., Graham R. A., Conacher H. B. S. and Verdier P. (1993) Survey of arsenic in total diet food composites and estimation of the dietary intake of arsenic by Canadian adults and children. Journal of AOAC International 76, 14±25. FDA (1997) Total arsenic data from an electronic database consisting of all results from total diet study market baskets collected from 1986 to 1994. Dataset. US Food and Drug Administration, Washington, DC. Francesconi K. A. and Edmonds J. S. (1994) Biotransformation of arsenic in the marine environment. In Arsenic in the Environment, Part I: Cycling and Characterization, ed. J. O. Nriagu, pp. 221±263. John Wiley & Sons, New York. Gunderson E. L. (1995) FDA total diet study, July 1986± April 1991, dietary intakes of pesticides, selected elements, and other chemicals. Journal of AOAC International 78, 1353±1363. Jelinek C. F. and Corneliussen P. E. (1977) Levels of arsenic in the United States food supply. Environmental Health Perspectives 19, 83±87. Mohri T., Hisanaga A. and Ishinishi N. (1990) Arsenic intake and excretion by Japanese adults: a 7-day dupli-
cate diet study. Food and Chemical Toxicology 28, 521± 529. Pennington and Jean A. T. (1992) Appendix BÐ Preparation and Cooking Instructions for Total Diet Study Foods, From Appendices for the 1990 Revision of the Food and Drug Administration's Total Diet Food List and Diets. Center for Food Safety and Applied Nutrition (CFSAN), US Food and Drug Administration (FDA). NTIS # PB92-176239. Phillips D. J. H. (1994) The chemical forms of arsenic in aquatic organisms and their interrelationships. In Arsenic in the Environment, Part I: Cycling and Characterization, ed. J. O. Nriagu, pp. 263±288. John Wiley & Sons, New York. Schoof R. A., Yost L. J., Crecelius E., Irgolic K., Goessler W., Guo H.-R. and Greene H. L. (1998) Dietary arsenic intake in Taiwanese districts with elevated arsenic in drinking water. Human and Ecological Risk Assessment 4, 117±135. Schroeder H. A. and Balassa J. J. (1966) Abnormal trace metals in man: arsenic. Journal of Chronic Disease 19, 85±106. Shiomi K. (1994) Arsenic in marine organisms: chemical forms and toxicological aspects. In Arsenic in the Environment, Part II: Human Health and Ecosystem Eects, ed. J. O. Nriagu, pp. 261±282. John Wiley & Sons, New York. Tsuda T., Inoue T., Kojima M. and Shigeru A. (1995) Market basket and duplicate portion estimation of dietary intakes of cadmium, mercury, arsenic, copper, manganese, and zinc by Japanese adults. Journal of AOAC International 78, 1363±1368. Uthus E. O. (1994a) Arsenic essentiality studies and factors aecting its importance. In Arsenic Exposure and Health, ed. W. R. Chappell, C. O. Abernathy and C. R. Cothern, pp. 199±208. Science and Technology Letters, Northwood, UK. Uthus E. O. (1994b) Estimation of safe and adequate daily intake for arsenic. In Risk Assessment of Essential Elements, ed. W. Mertz, C. O. Abernathy and S. S. Olin, pp. 273±282. ILSI Press, Washington, DC. Uthus E. O. and Seaborn C. D. (1996) RDA Workshop: New approaches, endpoints and paradigms for RDAs for mineral elements. Journal of Nutrition 126 (Suppl. Sep. 1996), S2452±S2459. USDA (1992) Nationwide Food Consumption Survey: Continuing Survey of Food Intakes by Individuals 1989±90. Dataset. US Department of Agriculture, Human Nutrition Information Service, Washington, DC. USDA (1993) Nationwide Food Consumption Survey: Continuing Survey of Food Intakes by Individuals 1990±91. Dataset. US Department of Agriculture, Human Nutrition Information Service, Washington, DC. USDA (1994) Nationwide Food Consumption Survey: Continuing Survey of Food Intakes by Individuals 1991±92. Dataset. US Department of Agriculture, Human Nutrition Information Service, Washington, DC. US EPA (1996) Method 1632, inorganic arsenic in water by hydride generation quartz furnace atomic absorption. EPA/821/R-95/028. US Environmental Protection Agency, Oce of Water, Oce of Science and Technology, Engineering and Analysis Division, Washington, DC. Yamauchi H. and Fowler B. A. (1994) Toxicity and metabolism of inorganic and methylated arsenicals. In Arsenic in the Environment, Part II: Human Health and Ecosystem Eects, ed. J. O. Nriagu, pp. 35±54. John Wiley & Sons, New York.