Article pubs.acs.org/JAFC
Arsenic Speciation in Australian-Grown and Imported Rice on Sale in Australia: Implications for Human Health Risk M. Azizur Rahman,*,† Mohammad Mahmudur Rahman,‡,§ Suzie M. Reichman,# Richard P. Lim,† and Ravi Naidu*,‡,§ †
Centre for Environmental Sustainability, School of the Environment, University of Technology Sydney, P.O. Box 123, Broadway, New South Wales 2007, Australia ‡ Centre for Environmental Risk Assessment and Remediation (CERAR), University of South Australia, Mawson Lakes Campus, Mawson Lakes, South Australia 5095, Australia § Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC-CARE), P.O. Box 486, Salisbury South, South Australia 5106, Australia # School of Civil, Environmental and Chemical Engineering, RMIT University, G.P.O. Box 2476, Melbourne, Victoria 3001, Australia ABSTRACT: Rice is an important route of arsenic (As) exposure to humans, especially populations with rice-based diets. Human health risk of As varies greatly with rice variety and country of origin. The purpose of the present study was to determine total and speciated As in Australian-grown and imported rice on sale in Australia to assess their health risk to consumers. The total As (tAs) concentrations in Australian-grown organic brown, medium grain brown, and organic white rice were 438 ± 23, 287 ± 03, and 283 ± 18 μg kg−1 dry weight (d wt), respectively. In Bangladeshi, Indian, Pakistani, and Thai rice imported and on sale in Australia, tAs concentrations were 56 ± 05, 92 ± 10, 82 ± 06 and 172 ± 24 μg kg−1, respectively. Asian rice contained mainly inorganic As (iAs; 86−99%), whereas 18−26% of the tAs in Australian-grown rice was dimethylarsinic acid (DMA). Relatively higher concentrations of tAs in Australian-grown rice than that in imported rice of Asian origin suggest that Australiangrown rice may be a health risk for the consumers. It was estimated that Australian-grown organic brown rice can contribute up to 98% of the FAO/WHO recommended maximum tolerable daily intake limit of iAs (2.1 μg kg−1 body wt day−1) for Asian immigrants. However, other Australian consumers including European immigrants are unlikely to be at risk to As from rice diets due to their lower rice consumption rates than that of Asian immigrants. The risk assessment showed that imported rice on sale in Australia was likely to pose a lower health risk to consumers than Australian-grown rice. KEYWORDS: arsenic speciation, rice, dietary intake, risk assessment, human health
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INTRODUCTION Elevated concentrations of arsenic (As) in groundwater pose major health problems for the people of Bangladesh, West Bengal (India), and several other countries of Southeast (SE) Asia.1−4 Arsenic-contaminated groundwater is used in South and SE Asian countries not only for drinking purposes but also for agricultural irrigation to grow crops such as rice and other food crops.5,6 Increasing levels of As in agricultural soils are due to irrigation with contaminated groundwater, and its uptake in rice and other food crops has become a real health issue in this region.5,7,8 Chronic effects of As toxicity to humans have been reported from many Asian countries through widespread water and crop contamination.3 Around 200 million people in South and SE Asia are estimated to be exposed to As contamination from water and foods.9 The recent incidence, where thousands of people are dying of arsenicosis and millions are potentially at risk, has led to renewed interest in As contamination worldwide.10 Arsenic pollution is also considered an important environmental issue in Australia;11 however, the health risks of As to the Australian people from foods have not been fully determined. Whereas many of the emerging As problems in the Asian region are due to mobilization of As originating from natural processes, those recorded in Australia include © 2014 American Chemical Society
contributions from both natural processes and anthropogenic activities associated with the use of arsenical pesticides, herbicides, sheep dip, atmospheric deposition, mining activities, waste disposal, and timber treatment processes.12 Mining activities have contributed to the contamination of soil and water in Western Australia and Victoria; however, other anthropogenic activities such as agriculture, forestry, and a variety of industrial processes have also contaminated soil and water on a localized scale.11 The most significant concern related to human health risks from As toxicity is worldwide food-chain transfer with the expansion of the global food trade, as millions more people are potentially exposed to increased concentrations of As in imported food in situations where local As contamination does not occur. A study showed that rice imported into the United Kingdom (UK) from Bangladesh contained high concentrations of As.13 These findings suggest that with supermarkets now sourcing their rice worldwide, As poisoning has potentially become a global problem exposing millions of Received: Revised: Accepted: Published: 6016
March 3, 2014 June 2, 2014 June 3, 2014 June 3, 2014 dx.doi.org/10.1021/jf501077w | J. Agric. Food Chem. 2014, 62, 6016−6024
Journal of Agricultural and Food Chemistry
Article
liquid chromatography unit (Agilent, Tokyo, Japan) equipped with a guard column and a Hamilton PRP-1000 separation column (250 × 4.1 mm) was used for the determination of As species in the samples. The samples were injected using an 1100 autosampler (injection volume was 50 μL). The mobile phase contained 30 mM NH4H2PO4 at pH 5.6, and the flow-rate was 1.0 mL min−1. The details of the instrumental conditions for As speciation were described elsewhere.15,16 All results in this paper are expressed on a dry weight (dw) basis. Analysis of Standard Reference Materials (SRMs) and QC/ QA. The analytical procedure was validated by analyzing certified standard reference material (SRM) of rice flour (SRM 1568a) from the National Institute of Standard and Technology (NIST), USA. The certified value of tAs in the SRM sample was 0.263 ± 0.012 μg g−1, whereas the measured value was 0.290 ± 0.03 μg g−1, indicating a recovery value of 110%. A reagent blank was also included in each batch of sample digestion and analysis to check the precision of the method. The detection limits for tAs and speciated As were evaluated by the analysis of solution matrix and determined to be 0.01 μg L−1 for tAs, 0.3 μg L−1 for AsV, 0.1 μg L−1 for AsIII and dimethylarsinic acid (DMA), and 0.2 μg L−1 for methylarsonic acid (MMA). The precisions of five replicate determinations were 2.7, 1.5, 1.7, and 2.4% for AsV, AsIII, DMA, and MMA, respectively. There is no certified material currently available for As speciation in rice. In the present study, we used an established and published extraction method for As speciation in rice grain using 2 M TFA.14 To validate the accuracy of our method and instrumental performance of As speciation analysis in rice grain sample, we analyzed As species in rice SRM (NIST 1568a) using the extraction procedures of 2 M TFA in a previous study, and the results were compared with those published by others.17 Our results on As speciation in NIST SRM rice sample were consistent with those of other studies. Dietary Exposure Estimates. According to the FAO/WHO,18 three basic approaches can be used to determine the dietary intake of chemical contaminants from foods: (i) total diet study, (ii) duplicate diet method, and (iii) diary study. These approaches combine the concentration of specific contaminants in food with individual consumption rate. In the present study, the total diet study approach was used to determine the dietary intake of As from Australian-grown and imported rice on sale in Australia according to the equation
consumers in countries not significantly affected by Ascontaminated groundwater. Thus, As in rice and the associated possible risks to human health can no longer be considered just a regional issue, but an important global issue. Australia is a multicultural country with significant numbers of immigrants from a range of countries including Asia and Europe. Rice is the staple food for a large number of Asian people living in Australia. Asian immigrants in Australia generally have strong preferences for rice imported from Asian countries, notably Bangladesh, West Bengal (India), Cambodia, and Vietnam. Because high concentrations of As in rice from As-endemic Asian countries have been reported,8 rice on sale in Australia imported from these countries could be an important source of dietary As exposure for Australian consumers, particularly the Asian immigrants who are normally high consumers of rice. The objective of this study was to determine total and speciated As concentrations in Australiangrown and imported rice on sale in Australia from Asian countries with significant As contamination issues, particularly Bangladesh and India, to establish whether average Australians and Asian immigrants are likely to be at risk of As exposure via their rice diets. The forms of As present in rice were measured to predict the degree of As toxicity from this food source. The dietary contributions of Australian-grown and imported rice on sale in Australia to the maximum tolerable daily intake (MTDI) of total and inorganic As for Australian consumers (average Australian, and Asian and European immigrants) were also estimated on the basis of rice consumption rates and body weights.
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MATERIALS AND METHODS
Chemicals and Reagents. All reagents were of analytical grade. Milli-Q (MQ) water (Milli-Q Plus system, Millipore, Bedford, MA, USA) was used throughout. Nitric acid (70%) and trifluoroacetic acid (TFA) were obtained from Mallinckrodt Chemicals, USA, and BDH Chemicals, UK, respectively. Sodium arsenite (NaAsO2), monosodium arsenate (Na 2 HAsO 4 ·7H 2 O), and monomethylarsonate (CH3AsNa2O3) were obtained from Sigma Chemicals, and dimethylarsinate ((CH3)2AsO(OH)) was from Chem Service Inc. Phosphate buffer (30 mM, pH 5.6) was prepared from ammonium dihydrogen orthophosphate (Ajax Chemicals, Australia), and the pH was adjusted by adding ammonium hydroxide (Biolab, Australia). The buffer solution was filtered through a 0.22 μm nylon membrane before use. Sample Collection and Preparation. Twenty-one samples representing 7 Australian-grown rice varieties and 51 samples of 17 different varieties of imported rice on sale in Australia were purchased from Australian and Asian shops in Sydney, Australia, during the month of January 2012. The samples were washed with tap water (three times) followed by deionized water (twice). The samples were then homogenized by grinding with a glass mortar and dried in an oven at 65 °C for 48 h before digestion for analysis. Total As and As Speciation Analysis. Total As in the samples was determined following the method of Rahman et al.4 Briefly, dried and ground samples (0.5 g) were each weighed into a digestion tube, and 5 mL of concentrated nitric acid (70%) was added and allowed to equilibrate overnight at room temperature. Then the tubes were placed on a digestion block (A. I. Scientific Block Digestion System AIM 500), and the temperature was increased from 75 to 140 °C over 8 h. Following digestion, tubes were removed, and after cooling, the samples were diluted to 20 mL with MQ water. Prior to analysis, all samples were filtered through 0.45 μm pore size filter paper (Whatman no. 41). The TFA extraction technique was used to determine As species in rice samples.14 An Agilent 7500c (Agilent Technologies, Tokyo, Japan) inductively coupled plasma mass spectrometer (ICP-MS) was used for the determination of total As (tAs) and As speciation. An Agilent 1100
DIAs = C tAs or iAs × CR rice
(1)
where DIAs is the dietary intake of As (μg person−1 day−1), CtAs is the tAs concentration (μg kg−1), CiAs is the iAs concentration (μg kg−1), and CRrice is the rice consumption rate (kg person−1 day−1). The health risk of total and inorganic As exposure from rice diet was estimated according to the equation DEAs = DI tAs or As ÷ BWav ind
(2) −1
−1
where DEAs is the dietary exposure (μg kg body weight day ), DItAs is the dietary intake of tAs (μg person−1 day−1), DIiAs is the dietary intake of iAs (μg person−1 day−1), and BWav ind is the average individual body weight of the consumers. Total dietary intake and health risk of tAs and As species were estimated for three major consumer groups in Australia: (i) average Australian, (ii) Asian immigrants, and (iii) European immigrants. These consumer groups were selected because they represent the major populations in the country who consume rice on a regular basis. As the body weights and rice consumption rates of Asian and European immigrants living in Australia are not available, the dietary intake and health risk of As were estimated based on average body weights and rice consumption rates of Asian and European adults as reported by Walpole et al.19 and Wailes and Chavez.19
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RESULTS AND DISCUSSION Total As Content in Australian-Grown and Imported Rice. The mean and range of tAs concentrations in Australiangrown rice were 270 and 188−438 μg kg−1, respectively. The highest tAs was found in organic brown rice (438 ± 23 μg 6017
dx.doi.org/10.1021/jf501077w | J. Agric. Food Chem. 2014, 62, 6016−6024
Journal of Agricultural and Food Chemistry
Article
Table 1. Concentrations of Total and Speciated Arsenic (Micrograms per Kilogram Dry Weight) in Australian-Grown and Imported Rice on Sale in Local Markets in Sydney, Australiaa As species origin Australia
local name and type of rice
n
brown rice (organic, medium grain) brown rice (whole, medium grain) brown rice (long grain) white rice (organic, long grain) Clever rice (long grain) white rice (long grain) sushi rice (sticky, Japanese style) all Australian rice (average)
3 3 3 3 3 3 3 21
total 438 287 198 283 257 241 188 270
± ± ± ± ± ± ±
inorganic 23 03 41 18 05 07 06
276 178 − 165 − − 177 −
± 25 ± 22 ± 08
± 13
% of total As
MMA
DMA
inorganic
methylated
all species
