Total and Inorganic Arsenic Concentrations in Rice Sold in Spain, Effect of Cooking, and Risk Assessments

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1 Environ. Sci. Technol. 2008, 42, Total and Inorganic Arsenic Concentrations in Rice Sold in Spain, Effect of Cooking, and Risk Assessments SILVIA TORRES-ESCRIBANO, MARIANA LEAL, DINORAZ VÉLEZ,* AND ROSA MONTORO Instituto de Agroquímica y Tecnología de Alimentos (CSIC), Apartado 73, 46100, Burjassot, Spain Received June 21, Revised manuscript received January 7, Accepted January 13, Rice can contain a relatively high amount of arsenic (As). We evaluated total and inorganic As concentrations in 39 samples of different types of rice sold in Spain. The analyses were performed in raw rice and in rice cooked by boiling to dryness in water spiked with As(V) (0.1 1 µg ml -1 ). In raw rice, inorganic As represented 27-93% of total As: total As ) ( µg g -1 dry weight (dw); inorganic As ) ( µg g -1 dw. After cooking, the rice retained between 45% and 107% of the As(V) added to the cooking water, and the inorganic As concentrations ranged between µg g -1 dw (0.1 µg ml -1 in the cooking water) and 3.89 µg g -1 dw (1.0 µg ml -1 in the cooking water). For raw rice, the inorganic As intake of the Spanish population (16 g raw rice/day) remains below the tolerable daily intake (TDI) proposed by the WHO (2.1 µg inorganic As/day/kg body weight). In rice cooked with water contaminated with As(V), this cereal intake is sufficient to attain the TDI. The results reveal the need to consider the determination of inorganic As and the influence of cooking when evaluating the risks associated with the consumption of rice. Introduction Rice is the dominant staple food for over half of the world s population, especially in Asian developing countries, contributing over 70% of the energy provided by their daily food intake (1). Rice is a complex matrix made up of carbohydrates, proteins, fats, fiber, and also minor components of great nutritional importance, such as minerals (P and K), vitamins (B1, B2, and niacin), phenolic compounds, and tocopherols with antioxidant functions (2, 3). However, rice also contains toxic trace elements, of which As, lead, and cadmium are the ones that have been most studied (1, 2, 4, 5). The few market basket surveys carried out in recent decades showed that total As concentrations in rice exceeded those found in other crops and vegetables (6 8). High concentrations of As have been detected in some samples sold in Taiwan (0.76 µg g -1 ) (9), Vietnam (0.697 µg g -1 )(1), and Australia (0.776 µg g -1 ) (1). The levels of As in the grain are influenced by the growing conditions, and it has been shown that there is an increase in the As with increasing As in irrigation water (10) or in soil (11). * Corresponding author phone: (+34) ; fax: (+34) ; deni@iata.csic.es). Arsenic is present in food, forming part of a large number of organic molecular species, some of which are considered to be innocuous [arsenobetaine (AB), arsenocholine (AC), trimethylarsine oxide (TMAO), and arsenosugars], whereas others are toxic [dimethylarsinic acid (DMA), monomethylarsonic acid (MA), and tetramethylarsonium ion (TETRA)]. Inorganic As species, As(III) and As(V), have also been detected and are regarded as carcinogens for humans (12). The FAO/WHO has established a provisional tolerable weekly intake (PTWI) of 15 µg inorganic As/week/kg body weight (13). Because As species widely differ in their degree of toxicity, speciation analysis is needed to provide a more reliable assessment of the health-risk associated with the consumption of food products. Inorganic As, MMA, and DMA have been detected in samples of rice (9, 14, 15). Despite the need for quantification of inorganic As in rice in order to assess the risk to humans, there are few studies of this aspect (7 9, 14 20). Also, for a more realistic evaluation of the risk, the effect of cooking on inorganic As concentrations must be studied. Rice is generally prepared by boiling it in water; if the water is contaminated by As, cooking increases the As concentration in the rice (15, 19, 21). The bioavailability for the human being (fraction of As that is solubilized and finally absorbed from the gastrointestinal tract into the systemic circulation) of the As species present in rice samples should also be considered (15). Rice production is heavily concentrated in Asia, with just four countries, China, India, Indonesia, and Bangladesh, accounting for nearly 70% of global production (22). In the European Union, Spain is the second largest producer of rice, ranking after Italy, with a production of t in 2003 and a cultivated area of ha in 2005 (23). Because of the high production in Spain and the substantial consumption of rice in some of its regions, the present study focuses on the As food safety of rice in a wide range of different types of rice sold and/or grown in Spain. The obtained results have been evaluated in the context of recent developments in research on As in rice. Materials and Methods Equipment. Arsenic was quantified with an atomic absorption spectrometer (AAS) model 3300 (Perkin-Elmer, Spain) equipped with an autosampler (AS-90, Perkin-Elmer), a flow injection hydride generation (FI-HG) system (FIAS-400, Perkin-Elmer), and an electrothermally heated quartz cell. Other equipment used included a lyophilizer (FTS Systems, USA), a sand bath (PL 5125, Raypa, Scharlau, Spain), a muffle furnace (K1253, Heraeus, Spain), a mechanical shaker (KS 125 Basic, IKA Labortechnik, Spain), and a centrifuge (Eppendorf 5810, Merck, Spain). Reagents. Deionized water (18.2 MΩ cm), obtained with a Milli-Q water system (Millipore Inc., Spain) was used for the preparation of reagents and standards. All chemicals used were of analytical or reagent grade. Glassware was treated with 10% (v/v) HNO 3 for 24 h and then rinsed three times with deionized water before being used. A standard solution of 1000 mg L -1 As(V) (Merck) was employed. Samples. Samples of different brands of rice (n ) 39) from various manufacturers, purchased in food stores in the city of Valencia (Spain), were analyzed (Table 1). The samples included the subspecies of rice with the highest production, japonica and indica, in their three types of grain (long, medium, and short), and subjected to different industrial processes (brown and white). The samples also included Basmati rice, Thai rice, wild rice, and mixtures of rice with other vegetables in which rice represented over 90% of the /es071516m CCC: $ American Chemical Society VOL. 42, NO. 10, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY Published on Web 04/11/2008

2 TABLE 1. Total Arsenic (As t ) and Inorganic Arsenic (As i ) Concentrations in Raw Rice (µg g -1, dry weight) a rice type grain country region As t As i % (As i )/(As t ) white short Spain ns ( ( ns ( ( León ( ( Valencia ( ( Valencia ( ( Valencia ( ( medium Spain ns ( ( long Spain ns ( ( Seville ( ( Tarragona ( ( Valencia ( ( thai long Thailand ns ( ( ns ( ( ns ( ( Basmati long India ns ( ( ns ( ( brown short Spain ns ( ( ns ( ( Seville ( ( Italy ns ( ( ns ( ( medium Spain ns ( ( ns ( ( Murcia ( ( Murcia ( ( Tarragona ( ( long Spain ns ( ( ns ( ( Italy ns ( ( ns ( ( Basmati long Spain ns ( ( USA ns ( ( ns ( ( red long Italy ns ( ( wild Canada ns <LD <LD mixture France ns b ( ( Spain ns c ( ( ns d ( ( ns e ( ( a Values are expressed as mean ( standard deviation (n ) 3); ns, not specified; LD, limit of detection. b Mixture of brown Basmati rice, unpolished red rice, and wild rice. c Mixture of short-grain rice, wild rice, red lentils, and adzuki beans. d Mixture of brown rice, Basmati rice, sesame, red lentils, green lentils, adzuki beans, and green soybeans. e Mixture of wild rice (25%) and parboiled long-grain rice (75%). total weight (sesame, red lentils, green lentils, adzuki beans, and green soybeans). The rice came from the four major rice-producing areas in Spain and from other countries. All samples (n ) 39) were analyzed raw, and some of them (n ) 34) were analyzed after a cooking process with As(V) contaminated water (0.1 1 µg ml -1 ). Twenty-seven samples were cooked once only with As(V) contaminated water. Seven representative samples of each type of rice (long white, white Thai, short brown, long brown, red, wild, and mixed) were cooked with two or three concentrations of As(V) in the range selected, raising the number of cooked rice samples to 46. The As(V) concentration in the water was randomly assigned. The cooking process emulated one of the processes normally applied in Spanish homes: boiling in water until all the liquid has evaporated (rice/water ) 1:4). After cooking, the samples were lyophilized. The raw samples and the lyophilized cooked samples were ground and then stored at 4 C until analysis. Total Arsenic Determination. The analysis was performed by flow injection-hydride generation-atomic absorption spectrometry (FI-HG-AAS) after a dry ashing step (24). Triplicate analyses were performed for each sample. The analytical characteristics of the method are as follows: detection limit ) µg g -1 dry weight (dw); precision ) 2%. Throughout the experiment, the quality assurance/ quality control of the measurement was checked by analyzing a rice flour certified reference material (SRM1568a, National Institute of Standards and Technology, NIST) with each batch of samples (n ) 15) (found value ) 0.29 ( 0.01 µgg -1, certified value ) 0.29 ( 0.03 µg g -1 ). Inorganic Arsenic determination. Analysis was performed by acid digestion, solvent extraction, and FI-HG- AAS (24). Triplicate analyses were performed for each sample. The analytical characteristics of the method are as follows: detection limit ) µg g -1 dw; precision ) 4%; As(III) recovery ) 99%, and As(V) recovery ) 96%. There are no reference materials with certified inorganic As concentrations, but various studies have analyzed inorganic As in rice flour, SRM1568a. This sample was analyzed with each series of samples (n ) 11), and the quality assurance/quality control of the measurement was checked by comparing the values found (0.110 ( µg g -1 dw) with the range reported in the literature ( µg g -1 dw) (9, 14, 15, 18, 20, 24, 25) ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 10, 2008

3 Results and Discussion Total Arsenic in Raw Rice. The total As concentrations (Table 1) range between and µgg -1 dw. The mean value in white rice (mean ( standard deviation ) ( µg g -1 dw; n ) 16) is close to the value found for brown rice (0.199 ( µg g -1 dw; n ) 18), although the range of concentrations is broader in white rice ( µg g -1 dw) than in brown rice ( µg g -1 dw). In Basmati rice, the total As concentrations found in brown rice are 2.5 times those found in white rice, although, as the samples are from different sources, it is not possible to attribute this difference to the treatment applied to the grain. However, Phuong et al. (1) report a substantial decrease in total As after polishing brown rice to obtain white rice. In the only sample of wild rice analyzed, the total As concentration is below the limit of detection of the method (0.026 µgg -1 dw). The mixtures of different types of rice and the mixtures of rice with other vegetables have mean concentrations of total As of ( µg g -1 dw (n ) 4). The type of grain (long, medium, or short) affects the cooking time and the texture of the rice after cooking. The consumer selects the type of grain on the basis of the dish to be prepared (salad, garnish, risotto, paella, etc.). In the total As concentrations of the samples analyzed in this study there are no outstanding differences associated with the type of grain. Concentrations in short-grain white rice (0.189 ( µg g -1 dw; n ) 6) overlap the concentrations found in long-grain white rice (0.154 ( µg g -1 dw; n ) 9). The only sample of medium-grain white rice analyzed has a high concentration (0.367 µgg -1 dw), close to the maximum values found in short-grain samples (0.406 µg g -1 dw) and longgrain samples (0.350 µg g -1 dw). In brown rice, the mean total As values overlap for short-grain (0.250 ( µg g -1 dw; n ) 5), medium-grain (0.192 ( µg g -1 dw; n ) 5), and long-grain (0.171 ( µg g -1 dw; n ) 8). For rice grown in Spain, the range of concentrations found ( µg g -1 dw; mean value ) µg g -1 dw, n ) 25) overlaps the range obtained from the few previous data concerning Spanish rice that are known to us ( µg g -1 dw; n ) 8) (9, 20, 26, 27). Most of the rice sold in Spain is also grown in this country, but in shops it is also possible to buy rice produced elsewhere. The mean concentration in the samples of European origin analyzed in this study (0.197 µg g -1 dw, n ) 31) is close to the mean value recently found in rice of the same origin (0.18 µg g -1 dw, n ) 7) by Williams et al. (9). The mean values obtained for rice produced in Italy (0.207 µgg -1 dw, n ) 5) and the USA (0.161 µg g -1 dw, n ) 2) lie within the range of concentrations previously reported: Italy µgg -1 dw, n ) 13 (2, 9, 26); USA µg g -1 dw, n ) 152 (8, 9, 14, 28). In Indian rice, the mean values [0.05 µg g -1 dw; n ) 12 (9, 20)] are similar to those found in our survey (0.063 µg g -1 dw, n ) 2). The concentrations that we found in Thai rice (0.148 µg g -1 dw, n ) 3) are also similar to those reported in the literature [0.11 µg g -1 dw, n ) 1(9)]. There are also reports of total As concentrations in raw rice from other sources: Vietnam, µgg -1 dw; n ) 56 (1); Australia, µgg -1 dw; n ) 11 (1); Canada, µg g -1 dw; n ) 7(6); Croatia, µg g -1 dw; n ) 38 (29); and Japan, µg g -1 dw; n ) 34 (29). It is in Asian arsenic-endemic areas that the largest number of studies of total As in rice have been carried out. Although it is true that there have been some rice samples from Bangladesh cultivated in arsenic-contaminated areas with high concentrations of total As [ µg g -1 dw (9, 30)], in most of the samples purchased in shops in Bangladesh [0.13 µg g -1 dw, n ) 15 (9)], or provided by Bangladeshi arsenic-affected families [0.136 µg g -1 dw; n ) 10 (31)], the total As concentrations are not very different from those found in European rice. The samples provided by Indian families [0.255 µgg -1 dw; n ) 54 (32, 33)] also have total As concentrations within the range reported for samples from Italy and the USA. The large quantity of rice produced in Asian arsenicendemic areas and the high total As concentrations detected in some samples led the FAO s Agriculture and Consumer Protection Department (34) to issue a warning in 2006 about the possible risk associated with this cereal. The report indicated that 0.05 µg g -1 dw is the customary total As concentration in rice sold in Europe and the USA and used that value as a reference concentration to evaluate the degree of contamination of Asian rice. However, that reference value may be considered low in view of all the data provided in the present article, which give a mean value of µg g -1 dw for total As in raw rice (Table 1). It would be advisable to go on expanding the database concerning total As in rice of different origins in order to generate appropriate conclusions and recommendations. Moreover, given that quantification of total As is insufficient for making a proper risk assessment, it is necessary to base conclusions on inorganic As concentrations. Inorganic Arsenic in Raw Rice. The nonchromatographic inorganic As method developed by our laboratory and used in the present study was recently used by the UK Food Standards Agency (FSA) for analysis of inorganic As in seaweed (35). This method quantifies the inorganic As and monomethylarsonic acid (MMA) in the sample. The overestimate produced by the quantification of MMA may be considered negligible because the MMA concentrations reported for rice are low (<0.02 µg g -1 dw) or undetectable (9, 14, 18 20, 26). Consequently, the joint quantification of MMA and inorganic As would not substantially affect risk assessment. The inorganic As concentrations found in this study (Table 1) range between µg g -1 dw and µg g -1 dw. The sample of wild rice is the only case in which inorganic As was not detected. In the literature there are very few data on inorganic As in rice. Until the publication in 2003 of a study of 40 samples of white rice sold in the USA (17), the data were limited to 15 samples (8, 14, 16). The recent study by Williams et al. (9) makes a significant contribution of data regarding samples sold in the USA (n ) 43). The data currently available indicate that inorganic As values in raw rice vary between 0.01 and µg g -1 dw (8, 9, 14 16, 18, 20, 26). In the present study, the percentage of total As represented by inorganic As varies between 27 and 93%. Similar percentages (11 91%) are reported in the literature (9, 14 16, 18, 20), and some of the cited studies show that the remaining As is provided by dimethylarsinic acid (DMA). In view of the great variation in the percentage of total As that corresponds to inorganic As, it is not advisable to extrapolate from total As concentrations in order to evaluate the toxicological risks associated with consumption of this cereal. The mean value of inorganic As (mean ( standard deviation) in white rice (0.085 ( µg g -1 dw; n ) 16) is less than the value found in brown rice (0.144 ( µgg -1 dw; n ) 18), with the mean concentration in brown rice being 1.7 times the mean concentration in white rice. The research conducted by Williams et al. (9) shows a similar relationship between these two types of rice (1.8), although the inorganic As concentrations are less in both cases: white (0.05 ( 0.03 µg g -1 dw; n ) 7); brown (0.09 ( 0.04 µg g -1 dw; n ) 17). The higher inorganic As concentration in brown rice might indicate that part of the contaminant is attached to components of the bran. We know of only three previous values for inorganic As concentration in Spanish rice: µg g -1 dw (26), 0.08 µg g -1 dw (9), and µg g -1 dw (20). The values of inorganic As obtained in the present study in the samples grown in Spain (mean value ) 0.12 µg g -1 dw, n ) 25) are, therefore, an important contribution for the establishment of a possible VOL. 42, NO. 10, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

4 FIGURE 1. Inorganic arsenic concentrations in raw rice and in the same rice cooked with water spiked with various concentrations of As(V) (0.1 1 µg ml -1 ). (a g) Samples of rice cooked with two or three concentrations of As(V). (a) Long white; (b) short brown; (c) long brown; (d) white Thai; (e) wild; (f) mixed; (g) red. reference value of inorganic As in rice produced in Spain. This value could be taken into account in the monitoring of the chemical safety of this cereal carried out by the authorities in Spain and other countries. Comparison of rice samples grown in various countries and sold in Spain shows that, as in the case of total As, among the samples with detectable inorganic As concentrations the lowest mean concentrations are found in rice from India and Thailand. We do not know of any published data concerning inorganic As concentrations in French rice; therefore, comparisons cannot be made. For the other countries of origin, however, values do exist. The previous data for Italian rice (mean value ) µg g -1 dw; n ) 5) (9, 26) are very similar to those found in the present study (mean value ) µgg -1 dw; n ) 5). The previous data for US rice (mean value ) 0.08 µg g -1 dw; n ) 18; µg g -1 ww; n ) 39) (8, 9, 14, 17) are close to those reported in this work (mean value ) µg g -1 dw; n ) 2). There is also considerable agreement in the values for rice grown in India [previous values 0.03 µg g -1 dw; n ) 12 (9, 20); this work µg g -1 dw; n ) 2)] and Thailand [previous values 0.08 µg g -1 dw, n ) 1(9); this work µg g -1 dw; n ) 3]. The mean values of inorganic As reported in commercial samples from Bangladesh [0.08 µg g -1 dw; n ) 15 (9)] are not much higher than those reported in the literature for other countries. The highest mean values reported in the literature are for rice from Taiwan: µg g -1 dw, n ) 3(16). According to the information available to us, China is the only country that has established a limit for the maximum inorganic As concentration in rice (36). That limit, 0.15 µg g -1 dw, is exceeded by 18% of the samples analyzed in this study. In view of the scarcity of studies of inorganic As in food, we consider that, before fixing legislative limits concerning inorganic As, the baseline studies should be amplified so that maximum values in accordance with reality may be established. Inorganic Arsenic in Cooked Rice. Figure 1 shows the inorganic As concentrations found after cooking different types of rice (n ) 34) in water spiked with various concentrations of As(V). The range of As(V) concentrations used (0.1 1 µg ml -1 ) emulates the customary concentrations in water in As-endemic areas (37). The inorganic As concentrations range between µg g -1 dw (0.1 µgml -1 in the cooking water) and 3.89 µgg -1 dw (1.0 µg ml -1 in the cooking water). Inorganic As represents 91% (mean value) of the total As, compared with 59% in raw rice. After cooking, the inorganic As concentration in the analyzed samples increases between 3 and 99 times, with a mean retention of 89 ( 13% (45 107%) of the As in the cooking water. In the present study the type of rice does not affect the ability to absorb inorganic As. A high retention (63 104%) of inorganic As in rice cooked with contaminated water has also been found by other authors (15, 19), who report that the percentage of water absorbed by the rice affects the inorganic As concentration in cooked rice, which is dependent on the type of rice and the way the rice is prepared (19). Two very interesting studies recently evaluated the influence on rice As retention of other cooking processes applied to the rice grain by Asian consumers (38, 39). Sengupta et al. (39) describe three different cooking methods, showing that when the rice is cooked in an excess of water and the remaining water is then discarded the retention of As (43%) is less than that observed in preparations in which rice is boiled in water until it is dry (72 and 99%) (39). Also, the use of parboiled or nonparboiled rice for the cooking process does not cause great variations in the retention of As (38). Consequently, it is possible to recommend cooking procedures that reduce the quantity of As absorbed by the rice. Although the use of water with the lowest possible quantity of As is the best option, it is not always available in arsenic-endemic areas. Priority should, therefore, be given to carrying out applied research with the aim of mitigating the toxicological risk in the customary living conditions of the affected population. Risk Assessment. As stated earlier, cooking in Ascontaminated water causes an increase in the inorganic As concentration in rice, which must be taken into account when evaluating the human health risk. This is reflected by the studies that estimate intake of inorganic As from the consumption of cooked food (vegetables and cereals) in arsenic-endemic areas of Chile (40) and Bangladesh (41). Except for some specific cases, the differences between the mean inorganic As concentrations in raw rice grown in the various countries are not very high, such that it is the consumption of the product (g/day), and not its concentration, that is the decisive aspect in the risk assessment for a particular population. Rice-based diets, very common in populations of Asian origin living in other continents, should be the object of toxicological evaluation with regard to ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 10, 2008

5 TABLE 2. Estimated Daily Intake of Inorganic Arsenic from Consumption of the Raw Rice Samples Analyzed and Comparison with the Tolerable Daily Intake (TDI) a inorganic As concentration in raw rice consumption intake minimum b : µg g -1 (dry weight) medium b : µg g -1 (dry weight) maximum b : µg g -1 (dry weight) 16 g/day c 0.43 µg inorganic As/day (0.3% TDI) 588 g/day d 15.9 µg inorganic As/day (10.6% TDI) 16 g/day c 1.82 µg inorganic As/day (1.2% TDI) 588 g/day d 67.0 µg inorganic As/day (44.7% TDI) 16 g/day c 4 µg inorganic As/day (2.7% TDI) 588 g/day d µg inorganic As/day (99.2% TDI) a TDI ) 2.1 µg inorganic As/kg body weight/day. For adults, assuming a weight of 70 kg, the TDI is 150 µg/day. b Minimum, medium and maximum concentration of inorganic As for all the raw rice samples analyzed in this study. c Consumption of raw rice by the Spanish population (42) d Mean consumption of paddy rice in South-East Asia (43). TABLE 3. Estimated Daily Intake of Inorganic Arsenic from Consumption of the Cooked Rice Samples Analyzed and Comparison with Tolerable Daily Intake (TDI) a inorganic As concentration in cooked rice minimum b : µg g -1 (wet weight) maximum c : 1.23 µg g -1 (wet weight) consumption cooked rice intake 225 g/day d 28.6 µg inorganic As/day (19% TDI) 750 g/day e 95.3 µg inorganic As/day (64% TDI) 1500 g/day f µg inorganic As/day (1.3 times the TDI) 225 g/day d µg inorganic As/day (1.8 times the TDI) 750 g/day e µg inorganic As/day (6.2 times the TDI) 1500 g/day f 1845 µg inorganic As/day (12.3 times the TDI) a TDI ) 2.1 µg inorganic As/kg body weight/day. For adults, assuming a weight of 70 kg, the TDI is 150 µg/day. b Minimum concentration: sample of white long-grain rice cooked with water containing 0.1 µg ml -1 As(V). Inorganic As concentration ) µg g -1 dw equivalent to µg g -1 wet weight (humidity of 70.3%). c Maximum concentration: sample of brown medium-grain rice cooked with water containing 1 µg ml -1 As(V). Inorganic As concentration ) 3.89 µg g -1 dw equivalent to 1.23 µg g -1 wet weight (humidity of 68.4%). d Consumption of cooked rice in Taiwan (16). e Consumption of cooked rice in West Bengal (32). f Consumption of cooked rice in Bangladesh (21). inorganic As intake, given that the members of these populations may be considered high consumers. In this evaluation, it would also be necessary to take the cooking process applied to the cereal into account, because it might alter the inorganic As concentration. In Spain, the mean consumption of raw rice by the Spanish population is 16 g/person/day (42). In Asian countries, consumption may be very high, attaining 588 g of paddy rice/ person/day in South-East Asia in 2005 (43). The data for consumption of cooked rice are scarce and indicate very different amounts for consumption of cooked rice: 225 g/day in Taiwan (16), 750 g/day in West Bengal (India) (32), and 1500 g/day in Bangladesh (21). We used these consumptions to evaluate inorganic As intake from the raw and cooked rice samples analyzed in the present study (Tables 2 and 3). To assess the risk for consumers, we compared the intakes obtained with the PTWI (15 µg inorganic As/kg body weight/week) (13). This value is equivalent to a tolerable daily intake (TDI ) PTWI/7 days) of 2.1 µg inorganic As/kg body weight/day. For adults, assuming a weight of 70 kg, the TDI is 150 µg/day. Table 2 shows the inorganic As intake for the consumption of raw rice in Spain (16 g/day). Regardless of whether the concentration in the rice is minimum, medium, or maximum, in no case does it attain the TDI. For the South-East Asian population (588 g/day), the minimum and medium inorganic As concentrations would result in intakes below the TDI (10.6 and 44.7%, respectively). In contrast, the rice with the highest inorganic As concentration (0.253 µg g -1 dw) would give an intake equivalent to 99.2% of the TDI, indicative of the risk that rice may represent in diets in which rice is the basic food, even if cooked in water with low levels of inorganic arsenic. As Williams et al. (9) stated, in regions with subsistence rice diets the As contributed by this grain is sufficient to attain the PTWI. In rice cooked with water contaminated with As(V) (Table 3), only the sample with the lowest concentration would give an inorganic As intake below the TDI. The other combinations would produce very high intakes. One must bear in mind that other cooked foods consumed by the population may also provide inorganic As. This, together with the contribution to inorganic As intake provided by the consumption of contaminated water, shows a more alarming panorama for arsenic-endemic areas than had previously been considered. Future research to be done in this area must also take account of the contribution of inorganic As from other foods in order to make a more realistic risk assessment. Finally, for a closer approximation of the risk assessment, the bioavailability (i.e., the fraction of absorbed As that reaches the systemic circulation) of inorganic As from cooked rice is an aspect to be taken into account. As far as we know, very little research has been done in this area. Ackerman et al. (19) and Laparra et al. (15) showed that the bioaccessibility (maximum soluble concentration in simulated gastrointestinal media) of inorganic As can reach 63 99% of the inorganic As present in cooked rice. Recently, the bioavailability of As in cooked rice has been estimated by in vitro (15) and in vivo models (44). The results obtained from the assays indicate the need to continue research along these lines in order to obtain a more realistic estimate of the possible risk resulting from dietary intake of this element. Acknowledgments This research was supported by project MCyT AGL , for which the authors are deeply indebted. S. Torres received a Personnel Training Grant from the CSIC in the I3P program cofunded by the European Social Fund to carry out this study. Literature Cited (1) Phuong, T. D.; Chuong, P. V.; Khiem, D. T.; Kokot, S. Elemental content of Vietnamese rice Part 1. Sampling, analysis and comparison with previous studies. Analyst 1999, 124, VOL. 42, NO. 10, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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