Environ. Sci. Technol. 2008, 42, 3867–3872
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, 2007. Revised manuscript received January 7, 2008. Accepted January 13, 2008.
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 ) 0.188 ( 0.078 µg g-1 dry weight (dw); inorganic As ) 0.114 ( 0.046 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 0.428 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) 963 900 022; fax: (+34) 963 636 301; e-mail:
[email protected]). 10.1021/es071516m CCC: $40.75
Published on Web 04/11/2008
2008 American Chemical Society
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 876 600 t in 2003 and a cultivated area of 119 000 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) HNO3 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 VOL. 42, NO. 10, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Total Arsenic (Ast) and Inorganic Arsenic (Asi) Concentrations in Raw Rice (µg g-1, dry weight)a rice type white
brown
grain
country
short
Spain
medium long
Spain Spain
thai long
Thailand
Basmati long
India
short
Spain
region
Ast
Asi
% (Asi)/(Ast)
ns ns León Valencia Valencia Valencia ns ns Seville Tarragona Valencia ns ns ns ns ns
0.406 ( 0.007 0.176 ( 0.004 0.133 ( 0.001 0.136 ( 0.009 0.141 ( 0.010 0.144 ( 0.019 0.367 ( 0.004 0.350 ( 0.016 0.179 ( 0.005 0.190 ( 0.005 0.098 ( 0.010 0.175 ( 0.008 0.141 ( 0.002 0.127 ( 0.003 0.067 ( 0.001 0.058 ( 0.008
0.133 ( 0.004 0.076 ( 0.002 0.089 ( 0.001 0.080 ( 0.001 0.093 ( 0.004 0.066 ( 0.001 0.145 ( 0.001 0.095 ( 0.003 0.101 ( 0.001 0.101 ( 0.002 0.062 ( 0.002 0.114 ( 0.008 0.087 ( 0.002 0.066 ( 0.002 0.030 ( 0.003 0.027 ( 0.002
33 43 67 59 66 46 40 27 56 53 63 65 62 52 45 47
0.252 ( 0.019 0.302 ( 0.024 0.152 ( 0.001 0.269 ( 0.005 0.273 ( 0.026 0.145 ( 0.005 0.158 ( 0.003 0.165 ( 0.001 0.204 ( 0.004 0.288 ( 0.013 0.230 ( 0.020 0.175 ( 0.009 0.179 ( 0.001 0.167 ( 0.012 0.148 ( 0.004 0.131 ( 0.009 0.191 ( 0.002 0.146 ( 0.003
0.173 ( 0.004 0.204 ( 0.018 0.113 ( 0.005 0.144 ( 0.001 0.176 ( 0.004 0.114 ( 0.008 0.138 ( 0.005 0.153 ( 0.001 0.183 ( 0.001 0.253 ( 0.006 0.150 ( 0.003 0.128 ( 0.003 0.138 ( 0.001 0.116 ( 0.002 0.081 ( 0.002 0.087 ( 0.002 0.128 ( 0.001 0.114 ( 0.008
69 68 74 54 64 79 87 93 90 88 65 73 77 69 55 66 67 78
Basmati long
Spain USA
red long
Italy
ns ns Seville ns ns ns ns Murcia Murcia Tarragona ns ns ns ns ns ns ns ns
wild
Canada
ns
