Scholarly article on topic 'Rice is a potential dietary source of not only arsenic but also other toxic elements like lead and chromium'

Rice is a potential dietary source of not only arsenic but also other toxic elements like lead and chromium Academic research paper on "Chemical sciences"

CC BY-NC-ND
0
0
Share paper
Academic journal
Arabian Journal of Chemistry
OECD Field of science
Keywords
{Rice / Arsenic / "Toxic elements" / "Essential elements" / "Almadinah Almunawarah"}

Abstract of research paper on Chemical sciences, author of scientific article — Amjad M. Shraim

Abstract Rice is a staple food and a good source of nutrition for half of the earth’s population including Middle Eastern countries. However, rice may accumulate hazardous levels of toxic elements. In KSA, rice is imported from many countries; some of which suffer from arsenic contamination in their groundwater and soil. Despite the large daily consumption of rice in KSA, no investigations on the contamination of rice sold there are published so far. Additionally, reports on the contamination of rice with other toxic elements are rare in the literature. To investigate this issue, a total of 84 rice samples were collected from local markets in Almadinah Almunawarah, KSA (n =70) and Brisbane, Australia (n =12) and analyzed for arsenic and other elements by ICP-MS. The mean concentrations (mgkg−1) for the KSA samples with concentrations >LOQ were 0.136 for As (range 0.026–0.464, n =70); Cd: 0.017 (0.003–0.046, n =64); Pb: 0.029 (0.003–0.218, n =40); Ni: 0.064 (0.042–0.086, n =5); Mg: 157 (51.8–777, n =70); Mn: 4.28 (0.960–10.9, n =70); Fe: 7.07 (1.9–55.1, n =70); Zn: 6.19 (1.15–13.5, n =70); Cu 1.28 (0.508–2.41, n =70); Se 0.202 (0.007–0.574, n =70); Cr: 0.057 (0.010–0.184, n =19); and Co: 0.012 (0.001–0.116, n =56). Several samples were found to contain at least one element in excess of the Chinese MCL (0.2mgkg−1for Cd, Cr, Pb, and iAs each). A large variation in element concentration was observed for samples of different origins. In comparison, the American rice accumulated the highest arsenic concentration (mean 0.257mgkg−1) followed by the Thai rice (mean 0.200mgkg−1), the Pakistani rice (mean 0.147mgkg−1), the Indian rice (mean 0.103mgkg−1), and finally the Egyptian rice (mean 0.097mgkg−1). Additionally, 3 individual samples from Surinam, Australia, and France contained arsenic concentrations (mgkg−1) of 0.290, 0.188, and 0.183. The findings of this investigation indicate that some of the rice varieties sold in KSA contain hazardous levels of arsenic and other toxic elements. For a better public health protection, concerned authorities are highly recommended to regularly monitor the concentrations of not only arsenic, but also other toxic elements (e.g. Cr, Cd, Pb) in rice grains.

Academic research paper on topic "Rice is a potential dietary source of not only arsenic but also other toxic elements like lead and chromium"

Arabian Journal of Chemistry (2014) xxx, xxx-xxx

King Saud University Arabian Journal of Chemistry

www.ksu.edu.sa www.sciencedirect.com

SPECIAL ISSUE: ENVIRONMENTAL CHEMISTRY

Rice is a potential dietary source of not only arsenic but also other toxic elements like lead and chromium

Amjad M. Shraim ^

Chemistry Department, Faculty of Science, Taibah University, Almadinah Almunawarah, Saudi Arabia

The University of Queensland, National Research Centre for Environmental Toxicology (Entox), Brisbane, Queensland, Australia Received 12 July 2013; accepted 4 February 2014

KEYWORDS

Rice; Arsenic; Toxic elements; Essential elements; Almadinah Almunawarah

Abstract Rice is a staple food and a good source of nutrition for half of the earth's population including Middle Eastern countries. However, rice may accumulate hazardous levels of toxic elements. In KSA, rice is imported from many countries; some of which suffer from arsenic contamination in their groundwater and soil. Despite the large daily consumption of rice in KSA, no investigations on the contamination of rice sold there are published so far. Additionally, reports on the contamination of rice with other toxic elements are rare in the literature. To investigate this issue, a total of 84 rice samples were collected from local markets in Almadinah Almunawarah, KSA (n = 70) and Brisbane, Australia (n = 12) and analyzed for arsenic and other elements by ICP-MS. The mean concentrations (mg kg-1) for the KSA samples with concentrations >LOQ were 0.136 for As (range 0.026-0.464, n = 70); Cd: 0.017 (0.003-0.046, n = 64); Pb: 0.029 (0.003-0.218, n = 40); Ni: 0.064 (0.042-0.086, n = 5); Mg: 157 (51.8-777, n = 70); Mn: 4.28 (0.960-10.9, n = 70); Fe: 7.07 (1.9-55.1, n = 70); Zn: 6.19 (1.15-13.5, n = 70); Cu 1.28 (0.508-2.41, n = 70); Se 0.202 (0.007-0.574, n = 70); Cr: 0.057(0.010-0.184, n = 19); and Co: 0.012 (0.001-0.116, n = 56). Several samples were found to contain at least one element in excess of the Chinese MCL (0.2 mg kg-1for Cd, Cr, Pb, and iAs each). A large variation in element concentration was observed for samples of different origins. In comparison, the American rice accumulated the highest arsenic concentration (mean 0.257 mg kg-1) followed by the Thai rice (mean 0.200 mg kg-1), the Pakistani rice (mean 0.147 mg kg-1), the Indian rice (mean 0.103 mg kg-1), and finally the Egyptian rice (mean 0.097 mg kg-1). Additionally, 3 individual

* Address: Chemistry Department, Faculty of Science, Taibah University, P.O. Box 30002, Almadinah Almunawarah, Saudi Arabia.

E-mail addresses: ashraim@taibahu.edu.sa, amjad@qu.edu.qa, a.shraim@uq.edu.au.

1 Current address: Chemistry and Earth Sciences Department, Faculty of Arts and Science, Qatar University, Qatar. Peer review under responsibility of King Saud University.

^jjfl I

Elsevier I Production and hosting by Elsevier

1878-5352 © 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University. http://dx.doi.org/10.1016/j.arabjc.2014.02.004

samples from Surinam, Australia, and France contained arsenic concentrations (mg kg-1) of 0.290, 0.188, and 0.183. The findings of this investigation indicate that some of the rice varieties sold in KSA contain hazardous levels of arsenic and other toxic elements. For a better public health protection, concerned authorities are highly recommended to regularly monitor the concentrations of not only arsenic, but also other toxic elements (e.g. Cr, Cd, Pb) in rice grains.

© 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University.

1. Introduction

Human beings are exposed to various types of chemical pollutants all the times. Metals and metalloids (e.g. lead, cadmium, mercury, chromium, and arsenic) are a special category of pollutants that can pose adverse health complications to living organisms (Nriagu, 1992; Stanley Manahan, 2000; Harrison, 2001; Jarup, 2003). For instance, chronic exposure to lead may result in kidney damage as well as memory and metal disorders especially in children (Fewtrell et al., 2004; Lamb et al., 2008; Xie et al., 2013). Chromium on the other hand is a human carcinogen. Moreover, long-term exposure to this metal results in various health effects including oxidative stress and DNA damage (Sato et al., 2003; Nickens et al., 2010; Khan et al., 2012). Arsenic, the main focus of this work, is a metalloid that resulted in a major health concern at a global scale (Ng, Wang et al., 2003; Zhu et al., 2008). This metalloid is very mobile in the environment and occurs naturally in several organic and inorganic species that vary significantly in toxicity. Based on epidemiological human evidence, inorganic arseni-cals (iAs) are classified as Group 1 human carcinogen (IARC, 1987; World Health Organization, 2001). Long term exposure to iAs, mainly in drinking water was shown to cause many illnesses including several types of cancers both in laboratory animals and humans (Ng et al., 1999; Karagas, 2001). On the other hand, many trace elements are considered as essential for the life of living organisms. However, the essentiality of such elements is valid only at certain levels of concentration, where they act as toxicants at higher levels or result in deficiency-related illnesses at lower concentrations. The essentiality vs. toxicity of several trace elements including Cr, Co, Cu, Fe, Mg, Mn, Se, and Zn has been thoroughly investigated by several scientists (Navarro-Alarcon and Lopez-Martinez, 2000; Goldhaber, 2003; Fraga, 2005; Nielsen, 2007; Blust, 2011; Broadley et al., 2012). A summary of the essentially/tox-icity of these elements is discussed in the following paragraphs with no further citation.

The essentiality and importance of Fe for the health of humans is undeniable. It is a very essential component of proteins that are involved in oxygen transport and very vital in regulating cell growth and their differentiation. Iron deficiency causes many health malfunctions such as anemia, fatigue, and decreased immunity. On the other hand exposure to excess concentrations of Fe is considered to be toxic.

Magnesium is one of several minerals that are needed in relatively large amounts by the human body mainly for healthy bones and teeth. It also plays important roles in the function of body enzymes and proteins. Deficiency in Mg may result in several health complications like muscle weakness, irregular heartbeat, high blood pressure, chronic alcoholism, and chronic diarrhea.

Zinc is an essential mineral and is largely involved in the body functions including the metabolism of the cell and is needed for the proper functioning of tens of body enzymes. It is also vital for the immune system, protein synthesis, DNA synthesis, and cell division.

Manganese is also an essential element with several benefits to the human body. It is important to the health of bones. It also acts as a co-enzyme assisting the metabolic activity in the body. Among the other benefits of Mn is its important role in the absorption of calcium and the proper functioning of the thyroid gland and sex hormones.

Selenium is a very important mineral and has many beneficial effects to the human body. This is mainly due to its anti-oxidant properties and its role in improving the immune system. High selenium blood levels have been liked with low rates of mortality from many types of cancer.

Copper is also one of the essential trace elements that are vital to the living organisms. It is vital to the proper functioning of body organs and its metabolic processes. Too little of this metal results in Cu deficiency with many related disorders including myelodysplastic syndrome, osteoporosis, cardiovascular disease, colon cancer, and many other chronic conditions. On the other hand exposure to excessive levels of Cu leads to health disorders such as stomach upset, nausea, diarrhea, headaches, and may cause liver and kidney damage.

Depending on its oxidation state, chromium can be either toxic or a source of minerals that is needed by the human body in trace amounts. Cr(VI) is toxic whereas Cr(III) is not. The latter is usually present in food.

Cobalt can also be beneficial for humans as it makes a major part in vitamin B12, but it can also be toxic as too high concentrations of this metal may result in negative implications to the human health.

The general population is exposed to arsenic and other toxic elements via ingestion of contaminated food or drink or through inhalation of polluted air (Shraim et al., 2003; Shrestha et al., 2003). Arsenic-contaminated water has affected the lives of hundreds of millions of people worldwide (Guo et al., 1997, 2001; Cantor et al., 2000; Kanel et al., 2005; Nickson et al., 2005; Ahamed et al., 2006; Shiber, 2007; Shinkai et al., 2007; Celik et al., 2008; Rahman et al., 2009). On the other hand, rice grains grown in arsenic-polluted soil or irrigated with arsenic-contaminated water have been recently reported to accumulate elevated levels of arsenic and can therefore contribute significantly to dietary arsenic intake (Mondal and Polya, 2008; Zavala et al., 2008; Zhu et al., 2008; Khan et al., 2009; Taskeen et al., 2009, Bhattach-arya et al., 2010a,b, Rahman et al., 2010). For example, Mondal and Polya reported that the contribution of rice to the total arsenic intake in some parts of India is as high as that of arsenic-contaminated drinking water, indicating that As-tainted rice can be a significant source of arsenic (Mondal and Polya, 2008).

Noticeably, literature on the contamination of rice with toxic elements other than arsenic is very rare and interest in rice as a potential source of exposure to arsenic is very recent. Rice is a staple food for more than half the world's population around the globe as it is a good source of carbohydrates, thiamin, vitamin B6, and some essential elements like magnesium, zinc and copper. The estimated share of total calories obtained from rice is 20.5% globally, 29.2% in low-income countries and 31.6% in Asia (Wailes, 2005). The world's total production of rice in 2009 reached 682 million metric tons, 80% of which came from the following countries: PR of China (29%), India (20%), Indonesia (9%), Bangladesh (7%), Vietnam (6%), Myanmar (5%), and Thailand (5%). The largest exporter of rice in 2009 was Thailand (29% of the world's rice export) followed by Vietnam (20%), USA and Pakistan (10% each), India (8%), and the rest of countries (23%) (FAO, 2010). Interestingly, many of the rice-producing/exporting countries suffer from arsenic contamination in their ground-water or soil (Bhattacharya et al., 2010a,b; Khan et al., 2010; Liang et al., 2010; Singh et al., 2010; Fu et al., 2011; Kuramata et al., 2011; Rahman and Hasegawa 2011 Review).

Rice is grown mainly under flooded conditions, a practice that can lead to accumulation of arsenic and possibly other toxic elements in rice grains and other parts of the plant when the soil or irrigating water is polluted(van Geen et al., 2006; Khan et al., 2010). Such type of accumulation is attributed mainly to anerobic conditions in soil, which result in higher arsenic mobilization rates and increase in its bioavailability to rice (Takahashi et al., 2004; Neumann et al., 2011).

Once absorbed, the health risks associated with exposure to arsenic from rice are expected to be similar to that of arsenic that comes from contaminated water (Juhasz et al., 2006; Booth, 2009). Although both adults and children are exposed to arsenic via rice, children and babies in particular are more vulnerable to such exposure due to differences in body mass. In addition to the arsenic burden from consuming rice grains in main meals, children are exposed to arsenic through consumption of rice-based products such as rice-milk and breakfast cereals as reported by Meharg et al. (2008), where elevated levels of iAs have been reported in many baby rice-products sold in the UK.

In the Kingdom of Saudi Arabia (KSA) and most other Middle Eastern countries rice is consumed on daily bases. Moreover, rice is not grown locally but the needs of the consumers are met via import, mainly from some Asian countries where high levels of arsenic are reported in groundwater resources and soil. To date, there are no reports in the literature about the arsenic contamination in rice grains sold in KSA. Additionally, reports on the contamination of rice with toxic elements, other than arsenic, are very scarce in the literature. The aim of this work was to report on the concentrations of arsenic and other toxic elements in rice and rice-products sold in the local markets of Almadinah Almunawarah. Some rice samples were also collected from local markets in Brisbane (Australia) and others were obtained from arsenic-endemic areas in Bangladesh.

2. Experimental

2.1. Chemicals and reagents

Ultrapure water (18.2 M cm, Milli-Q, Gradient with Elix10, Millipore, USA) was used in all preparations and dilutions;

nitric acid (90% fuming) was obtained from Fisher Scientific (New Jersey, USA); hydrogen peroxide (30%) was purchased from Panreac Quimica (Barcelona, Spain); ICP-MS multi-element calibration standards from Agilent Technologies (10 pg mL-1 each, USA); water analytical reference material (TM-25.3) from National Water Research Institute, Environment Canada; and rice certified reference material (IRMM-804) was obtained from the Institute for Reference Materials and Measurements (European Commission, Geel, Belgium).

2.2. Sample collection, digestion, and analysis

A total of 84 rice grain samples were analyzed: 70 samples were collected in Feb 2012 from local markets in Almadinah Almu-nawarah, KSA; 12 samples were collected in July 2010 from Brisbane, Australia; and 2 rice samples were obtained in person from arsenic-endemic areas in Bangladesh.

A representative portion (~50 g) from each sample with no prior treatment was powdered using a hand analytical mill (IKA A11 basic, Germany). About 1.0000 g of the powder was accurately weighed, placed in a Teflon vessel and digested using a microwave oven (Ethos 1 Advanced Microwave Digestion System from Milestone, Italy) as follows: 5.00 mL of conc. nitric acid was added followed by 5.00 mL of water and 1.00 mL of hydrogen peroxide (30%). The steps of the digestion program were: 1st step was run for 3 min at 80 0C, 2nd step: 9 min at 145 oc, 3rd step: 4 min at 180 0C, and last step: 15 min at 180 oc. After cooling, the clear solutions were diluted to 50.00 mL with water. With every batch of digested samples, a certified rice reference material and a blank were used and treated in the same way as the samples. About 10 mL of each digested solution was filtered through a 0.2 pm membrane filter just prior to ICP-MS analysis.

An Inductive Coupled Plasma Mass Spectrometer (ICP-MS, 7500cx, Agilent Technologies, Japan) was used for the quantitative measurement of elements. The operational parameters applied are listed in Table 1.

The figures of merit of the analytical method were assessed using limits of quantitation (LOQ), calibration verification checks, accuracy, and precision.

Blank and multi-element calibration solutions of 1.00, 2.00, 2.50, 5.00, 10.0, 25.0, 50.0, and 100.0 pg L-1 were used to calibrate the instrument. A calibration verification check (CVC-50) using a 50.0 pgL-1 solution prepared from a stock solution different from that used for the preparation of the calibration solutions was utilized. A seven-sample blank replicate analysis was used to calculate the limit of quantitation (LOQ = standard deviation (SD) x10). The precision of the method was assessed using replicate analysis of 3 different rice samples; whereas certified reference materials were used for evaluating the accuracy.

3. Results and discussion

3.1. Quality Control

The outcome of the quality control assessment is listed in Table 2. The LOQ range for the elements of interest is 0.002-0.117 pgL-1. The R2 values for the calibration curves are better than 0.999 for all elements except for Fe (0.9981). The mean values and standard deviations for the elements in

Table 1 ICP-MS operating parameters.

Sampler Ni, Standard

Skimmer Ni, Standard

Nebulizer Micromist, Standard

Plasma torch Quartz, 2.5 mm,

Standard

Integration time (s X points)

He mode

Mg 0.05 x 3

Cu 0.50 x 3

Cr, Ni, As, Se 1.0 x 3

Mn, Fe, Co, Zn, 0.10 x 3

No gas mode

Cd 1.0 x 3

Pb 0.10 x 3

Tune parameters

RF power (W) 1550

Sample depth (mm) 8.4

Carrier gas (Lmin-1) 0.95

Makeup gas (L min-1) 0.2

Extract 1 (V) 1.0 (2.8 for He gas

reaction mode)

Extract 2 (V) -139.5

Discriminator (mV) 8.0

Reaction gas (He, mL min-1) 4.0

CeO/Ce (156/140,%oxide ratio) 1.05

Ce++/Ce (70/140,%doubly charged ratio) 2.12

%RSD for m/z: 7, 59, 89, 205 <2

Spray chamber temperature (°C) 2.0

Nebulizer pump (rps) 0.1

the CVC-50 solution are 50.2-54.5 and 0.580-3.62 igL-1, respectively. The accuracy results for the two certified reference materials (rice and water) varied between 75% and 102%. On the other hand the precision values measured as %RSD for all replicate analyses (i.e. CRM's and 3 rice samples) were between 2.1% and 14.3%. Overall, the outcome of the quality control tests is good ensuring high quality results.

3.2. Concentrations of arsenic and other toxic elements in rice samples

The concentrations of elements along with a statistical summary in rice samples are listed in Table 3.

The mean arsenic concentration in the KSA 70 rice samples was 0.136 mg kg-1 with a standard deviation (stdev) of 0.086 mg kg-1, a median of 0.107 mg kg-1, and a range of 0.026-0.464 mg kg-1. The arsenic concentrations were found to vary widely with the country of origin as shown in Table 4. In comparison, the American rice contained the highest arsenic concentration mean of 0.257 mg kg-1 followed by the Thailand rice (mean 0.200 mg kg-1), then the Pakistani rice (mean 0.147 mg kg-1), then the Indian rice (mean 0.103 mg kg-1), and finally the Egyptian rice (mean 0.097 mg kg-1). Additionally, 3 individual rice grain samples from Surinam, Australia, and France contained arsenic concentrations of 0.290, 0.188, and 0.183 mg kg-1.

On the other hand, the mean arsenic concentration in the rice samples collected from Brisbane markets (refer to Table 3) is 0.092 mg kg-1 (n =12, SD 0.021 mg kg-1, median 0.100 mg kg-1, and range 0.054-0.116 mg kg-1).

To assess the suitability of food items for human consumption, their levels of elements have to be checked against relevant established maximum contaminant levels (MCLs). Interestingly, the only available MCLs for toxic elements in rice grains are those established by the PR of China (Ministry of Health, 2012). Out of the elements analyzed in this study, MCL values were reported only for cadmium, chromium, lead, and inorganic arsenic (iAs), with a value of 0.2 mg kg-1 each.

Rice has been shown to accumulate various forms of arsenic like arsenite, arsenate, methylarsonic acid and dimethyl-arsinic acid that differ in toxicity to living organisms. The first two species (iAs) are more toxic than the other two species (Hughes, 2002; Hirano et al., 2004). Although only total arsenic concentrations were determined in this investigation, special attention has be given to rice samples with arsenic concentrations >0.200 mg kg-1 (i.e. 4 samples from USA with As concentrations of 0.293, 0.363, 0.463, and 0.464 mg kg-1; 4

Table 2 Figures of merit of the analytical method (nc: no certified value provided).

24Mg 52Cr 55Mn 56Fe 59Co 60Ni 63Cu 66Zn 75As 78Se mCd 208Pb

LOQ, igL-1, n 7 0.117 0.005 0.025 0.093 0.002 0.030 0.019 0.077 0.003 0.011 0.003 0.011

Water CRM, ig L-'

Obtained mean 2712 20.7 23.8 26.9 25.9 14.58 25.2 42.6 29.1 29.4 28.2 26.91

(SD), n 4-5 135.3 0.92 1.02 2.39 1.06 0.41 1.25 0.46 0.55 0.36 0.42 0.54

Certified mean - 24.5 25.4 29.5 28.0 15.5 27.6 41.9 27.6 27.9 24.0 27.8

Rice CRM, mg kg-'

Obtained mean 862.3 0.106 29.73 9.87 0.013 1.75 2.50 16.63 0.046 0.029 1.20 0.427

(SD), n 4-5 (10.1) (0.012) (1.03) (0.55) (0.001) (0.07) (0.40) (0.52) (0.008) (0.001) (0.02) (0.026)

Certified mean nc nc 34.2 nc nc nc 2.72 23.1 0.049 0.038) 1.61 0.42

(SD) - - (2.3) - - - (0.24) (1.9) (0.004) (0.004) (0.07) (0.07)

Precision, n 6, mg kg" -1

Sample no. R72 106.9 0.048 6.48 2.37 0.009 <LOQ 0.954 3.47 0.188 0.061 <LOQ <LOQ

Mean (SD) (6.61) (0.032) (0.41) (0.81) (0.002) - (0.11) (0.23) (0.016) (0.006) - -

Sample no. R73 130.9 <LOQ 4.03 2.38 0.008 <LOQ 0.856 4.15 0.079 0.104 0.011 <LOQ

Mean (SD) (2.88) - (0.13) (0.14) (0.001) - (0.06) (0.24) (0.006) (0.008) (0.001) -

Sample no. R74 144.2 <LOQ 3.79 2.23 0.006 <LOQ 0.987 4.06 0.074 0.131 0.016 <LOQ

Mean (SD) (15.4) - (0.31) (0.29) (0.0004) - (0.07) (0.28) (0.005) (0.009) (0.001) -

Table 3 Concentrations of elements (mg kg ^ in all rice samples.

Sample no. Grain type/color Origin

24Mg 52

Concentrations in rice samples collected from Almadinah Almunawarah markets, KSA

Long/White

Long/White

Medium/White

Long/White

Long/Yellow

Long/Yellow

Long/Yellow

Long/Yellow

Long/Yellow

Medium/White

Medium/White

Round/White

Round/White

Round/White

Long/Brown

Long/Brown

Medium/Red

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/Yellow

Long/Yellow

Long/Yellow

Long/Yellow

Long/Yellow

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/White

Long/Yellow

Long/White

USA USA USA USA USA USA USA USA USA Egypt;

Egypt; Egyp;

Egyp; Egyp;

India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India India

106 98.1 208 121 198 191 139 169

217 173 86.5 118 51.8

123 777 732 205 108

124 168 124 156

143 172 159 121

155 95.5 103 127

156 162 106 168

133 185

163 222

218 167 162

144 184 150

139 201 177

164 131 148

Pakistan 67.1

Pakistan 72.7

Pakistan 126

Pakistan 117

Pakistan 106

Pakistan 123

Pakistan 108

Pakistan 127

Pakistan 167

Thailand 77.3

0.026 <LOQ <LOQ 0.060 <LOQ <LOQ 0.144 <LOQ <LOQ <LOQ <LOQ <LOQ 0.044 0.010 0.056 <LOQ <LOQ 0.089 0.026 0.079 0.017 0.022 0.015 0.053 <LOQ <LOQ <LOQ <LOQ 0.184 0.038 <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ 0.081 <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ 0.058 0.026 <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ

3.90 0.964

8.47 4.54

7.43 6.28

4.00 4.76 6.66 7.30 5.62 6.21 2.40 3.32 10.4 10.9 3.07

1.44 4.35 3.82

4.48 1.58 4.80 5.18

3.76 4.13 1.96 1.17 1.44 1.52 2.26 4.54 4.01

1.77 5.17

1.73 5.35 5.62 4.89 2.23 3.79

4.66 4.57

5.08 2.40 1.84 1.93 4.03 1.40 4.72

5.72 0.983

4.91 5.87 4.60 1.86 2.57

2.77 4.10

13.6 4.84

47.0 5.35

4.33 4.75

2.17 2.01

11.7 10.3

2.58 4.46

2.63 2.99 2.45 3.44

6.83 2.54

55.1 3.49 8.09 9.75 7.60

7.34 5.93 6.23

5.54 8.62 2.23 5.84 5.02 7.49 8.34

7.78 6.28

2.38 4.18

2.91 3.97

4.39 11.3

3.59 6.08

8.60 9.97 5.52 3.15

0.007 0.007 <LOQ 0.008 0.013 0.010 0.010 0.001 0.004 0.003 <LOQ 0.007 0.007 0.008 0.010 0.007 0.020 0.008 0.005 0.006 0.014 0.004 0.005 0.006 0.019 <LOQ <LOQ <LOQ 0.111 0.006 <LOQ 0.004 0.002 0.002 0.010 0.004 0.003 0.005 0.003 <LOQ 0.027 <LOQ 0.003 0.006 <LOQ 0.004 0.012 0.009 0.116 <LOQ 0.008 0.003 <LOQ <LOQ 0.011 0.003 0.005 0.008 0.005 0.006 <LOQ 0.012

<LOQ <LOQ <LOQ <LOQ <LOQ <LOQ 0.044 <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ 0.085 <LOQ <LOQ 0.063 <LOQ <LOQ <LOQ <LOQ <LOQ 0.042 <LOQ <LOQ <LOQ <LOQ 0.086 <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ

0.929 0.572 1.38 0.755

1.30 1.35 0.893 0.879 1.55

1.31 1.25

1.43 0.911 1.35 1.77 1.66 0.811 1.20 1.17

1.16 1.40 1.09 1.55

1.55 1.01 1.11 1.35 1.08 1.05

1.40 1.52 1.38 1.51 1.62 1.47

1.71 1.43 1.54

1.45 0.987

1.32 1.21 1.49 1.61 1.19 1.66 0.856 1.11

1.56 2.08 0.917

1.57 1.23 1.60

2.41 1.51 0.993

2.46 1.56 6.07 2.16 5.49 5.15

3.20 5.66 5.12 5.81

5.81 6.72 2.39

3.47 7.12

11.0 2.72 1.78 2.00

4.46 4.97 4.04 5.49

8.21 9.89 5.89

7.07 1.43 1.85 3.85 3.84 5.26 8.01 8.34 9.30 4.41 9.14 3.75 9.89 8.92

10.5 4.03 4.06

9.78 8.74

8.47 3.87

2.84 8.72

11.4 1.15 10.9 8.24 11.2

4.08 2.77

0.164 0.155 0.139 0.127 0.463 0.464 0.145 0.363 0.293 0.123 0.094 0.154 0.039 0.074 0.060 0.089 0.088 0.082 0.085 0.104 0.026 0.079 0.061 0.068 0.099 0.046 0.068 0.065 0.071 0.104 0.220 0.114 0.120 0.120 0.100 0.145 0.226 0.134 0.212 0.103 0.108 0.097 0.134 0.074 0.084 0.060 0.066 0.077 0.105 0.115 0.079 0.228 0.071 0.086 0.061 0.079 0.116 0.091 0.187 0.106 0.141 0.185

0.119 0.022 0.043 0.176 0.402 0.338 0.127 0.101 0.260 0.032 0.021 0.044 0.007 0.017 0.202 0.205 0.084 0.116 0.258 0.150 0.167 0.169 0.253 0.154 0.239 0.488 0.286 0.360 0.053 0.223 0.415 0.514 0.298 0.300 0.413 0.285 0.389 0.204 0.273 0.262 0.212 0.343 0.269 0.131 0.574 0.429 0.171 0.352 0.306 0.417 0.104 0.200 0.109 0.162 0.052 0.113 0.155 0.147 0.151 0.188 0.250 0.050

0.006 <LOQ 0.008 0.008 0.019 0.013 0.005 0.009 0.020 0.004 0.003 0.005 <LOQ <LOQ 0.018 0.032 0.016 0.006 0.005 0.007 0.011 0.003 0.014 0.008 0.018 0.026 0.023 0.020 0.046 <LOQ 0.006 0.014 0.019 0.031 0.023 0.025 0.013 0.019 0.014 0.027 0.025 0.030 0.016 0.016 0.023 0.020 0.022 0.012 0.034 0.017 0.011 0.005 0.032 0.036 <LOQ 0.042 0.011 0.039 0.007 0.024 0.010 0.020

0.014 <LOQ <LOQ 0.048 0.036 0.098 0.021 <LOQ 0.032 <LOQ 0.015 0.031 <LOQ 0.017 0.025 0.015 0.067 0.022 0.031 0.033 0.014 0.017 <LOQ 0.015 <LOQ <LOQ <LOQ <LOQ 0.218 0.020 <LOQ 0.024 0.039 <LOQ 0.014 <LOQ 0.016 <LOQ 0.019 <LOQ 0.015 <LOQ 0.042 <LOQ 0.014 <LOQ 0.003 <LOQ 0.015 <LOQ <LOQ 0.011 <LOQ <LOQ 0.022 <LOQ 0.018 <LOQ 0.019 0.022 <LOQ 0.028 ntinued)

Table 3 (continued)

Sample no . Grain type/color Origin 24Mg 52Cr 55Mn 56Fe 59Co 60Ni 63Cu 66Zn 75As 78Se mCd 208Pb

R66 Long/White Thailand 78.7 <LOQ 7.52 5.17 0.011 <LOQ 0.960 13.5 0.200 0.093 0.015 0.015

R67 Long/White Thailand 65.6 <LOQ 4.43 3.75 0.014 <LOQ 0.902 9.35 0.181 0.063 0.007 <LOQ

R68 Long/White Thailand 86.9 <LOQ 6.16 6.65 0.018 <LOQ 0.931 10.7 0.195 0.075 0.007 0.012

R69 Long/White Thailand 101 <LOQ 8.09 4.57 0.022 <LOQ 0.626 11.5 0.250 0.100 0.008 <LOQ

R70 Long/White Thailand 83.1 <LOQ 4.13 7.79 0.023 <LOQ 0.508 7.05 0.190 0.055 0.013 0.022

R10 Medium/White Australia 107 0.048 6.48 2.37 0.009 <LOQ 0.954 3.47 0.188 0.061 <LOQ <LOQ

R64 Long/White Surinam 156 <LOQ 3.67 5.65 0.010 <LOQ 1.21 12.4 0.290 0.096 0.008 0.018

R16 Long/White France 182 <LOQ 4.65 4.95 <LOQ <LOQ 1.56 8.61 0.183 0.247 0.013 <LOQ

Statistical ssummary for rice samples collected from Almadinah Almunawarah markets, KSAa

n 70 19 70 70 56 5 70 70 70 70 64 40

mean 157 0.057 4.28 7.07 0.012 0.064 1.28 6.19 0.136 0.202 0.017 0.029

SD 111 0.045 2.17 8.11 0.020 0.021 0.339 3.21 0.086 0.133 0.010 0.035

median 139 0.048 4.45 5.53 0.007 0.063 1.32 5.57 0.107 0.174 0.015 0.020

min 51.8 0.010 0.96 1.95 0.001 0.042 0.508 1.15 0.026 0.007 0.003 0.003

max 777 0.184 10.9 55.1 0.116 0.086 2.41 13.5 0.464 0.574 0.046 0.218

Concentration in rice samples collected from Brisbane, Australia

R71 Medium/White Australia 162 0.063 11.9 3.68 0.017 1.64 2.55 10.2 0.106 0.066 0.034 0.055

R72 Medium/White China 156 0.075 8.36 4.27 0.018 1.64 2.30 10.9 0.093 0.032 0.002 0.296

R73 Medium/White China 95.3 0.390 11.8 3.57 0.013 1.66 1.73 8.65 0.104 0.028 0.013 0.016

R74 Medium/White China 133 0.094 7.85 4.45 0.015 1.76 1.63 10.5 0.064 0.028 0.028 0.354

R75 Long/White Pakistan 121 0.065 7.04 3.52 0.017 1.77 3.94 10.8 0.065 0.079 0.043 0.025

R76 Long/White Thailand 72.7 0.055 6.13 1.75 0.017 1.64 1.54 10.8 0.101 0.035 0.019 0.025

R77 Long/White Thailand 89.0 0.130 7.34 3.98 0.026 1.63 1.61 10.9 0.112 0.056 0.150 0.300

R78 Long/White Thailand 63.7 0.095 6.15 2.59 0.017 1.54 1.93 10.6 0.099 0.032 0.011 0.236

R79 Long/White Thailand 109 0.047 10.6 6.47 0.019 1.76 1.27 13.0 0.080 0.031 0.046 0.054

R80 Long/White Thailand 96.6 0.033 8.77 2.70 0.022 3.01 5.32 18.3 0.116 0.040 0.015 0.019

R81 Medium/White USA 155 0.041 13.1 3.67 0.017 2.13 6.23 13.5 0.106 0.030 0.008 0.041

R82 Medium/White USA 216 0.075 14.8 2.99 0.017 1.72 2.53 8.44 0.054 0.040 0.095 0.019

Statistical summary for rice grain samples collected from Brisbane, Australia 1

n 12 12 12 12 12 12 12 12 12 12 12 12

mean 123 0.097 9.49 3.64 0.018 1.83 2.72 11.4 0.092 0.041 0.039 0.120

SD 44 0.096 2.88 1.17 0.003 0.402 1.61 2.60 0.021 0.017 0.043 0.133

median 115 0.070 8.57 3.62 0.017 1.69 2.12 10.8 0.100 0.033 0.024 0.047

min 63.7 0.033 6.13 1.75 0.013 1.54 1.27 8.44 0.054 0.028 0.002 0.016

max 216 0.390 14.8 6.47 0.026 3.01 6.23 18.3 0.116 0.079 0.150 0.354

R83 Medium/Brown Bangladesh 315 0.909 9.64 24.7 0.029 2.03 4.91 5.44 0.143 0.062 0.004 0.089

R84 Medium/white Bangladesh 128 0.491 3.64 14.3 0.020 1.50 2.42 5.71 0.304 0.028 0.015 0.020

n gives the number of samples with concentrations pLOQ (limit of quantitation).

a Only the results that are pLOQ were included in the statistics.

samples from India: range 0.212-0.228 mg kg-1; 2 from Thailand: 0.200 and 0.250 mg kg-1; and 1 from Surinam: 0.290 mg kg-1). This type of variation in As concentration in rice grains was also observed by many investigators. For instance, a 7-fold difference in As concentration was reported for 901 white rice samples collected from 10 countries in 4 continents. The median arsenic concentration for the Egyptian and Indian rice was the lowest with values of 0.04 and 0.07 mg kg-1, respectively, while the highest content was reported for the USA and France rice samples with median values of 0.25 and 0.28 mg kg-1, respectively (Meharg et al., 2009). High levels of As have also been reported for rice grains grown in some parts of the USA (e.g. reported means for Texas and Arkansas rice were 0.258 and 0.190 mg kg-1) (Zavala and Duxbury, 2008). Some Chinese rice has also been shown to accumulate high levels of As, where a mean arsenic concentration of 0.092 mg kg-1 (range 0.005-0.309 mg kg-1) was reported for 282 brown rice grains collected from Hainan Island, China (Fu et al., 2011). Similarly, a high As mean con-

centration of 0.223 mg kg-1 (range 0.109-0.376 mg kg-1) was reported for 44 different rice samples from Brazil (Batista et al., 2011). Relatively high As concentrations have also been reported for 95 rice samples collected from Southwestern Bangladesh with a mean As concentration of 0.23 mg kg-1 and a coefficient of variation of 53 (Rahman et al., 2010). However, higher levels of arsenic have been reported for rice samples collected from Bangladeshi arsenic-endemic areas (mean As concentration was 0.358 mg kg-1, range 0.046-1.110 mg kg-1, n = 46) (Smith et al., 2006). This has also been supported by the results of the 2 rice samples collected from As-endemic areas in Bangladesh as shown at the end of Table 3 (As concentrations of 0.143 and 0.304 mg kg-1). Rice grain samples from arsenic-endemic areas in West Bengal, India were also reported to contain high concentrations of As with a mean value of 0.45 mg kg-1 (n = 21, range 0.19-0.78 mg kg-1) for Boro rice and a mean concentration of 0.33 mg kg-1 (n = 8, range 0.06-0.60 mg kg-1 for Aman rice (Bhattacharya et al., 2010a,b).

Table 4 Mean, standard deviation (SD), median, and range concentrations (mg kg 1) for some toxic elements in the rice samples sold

in Almadinah Almunawarah, KSA arranged by country of origin.

Country of origin n a Mean ± SD Median Range

Arsenic

USA 9/9 0.257 ± 0.142 0.164 0.127-0.464

Thailand 6/6 0.200 ± 0.025 0.192 0.181-0.250

Pakistan 9/9 0.147 ± 0.055 0.151 0.052-0.250

India 38/38 0.103 ± 0.048 0.093 0.026-0.228

Egypt; 5/5 0.097 ± 0.044 0.094 0.039-0.154

Surinam 1/1 0.290

Australia 1/1 0.188

France 1/1 0.183

Cadmium

USA 8/9 0.011 ± 0.006 0.006 0.005-0.020

Thailand 6/6 0.012 ± 0.005 0.010 0.007-0.020

Pakistan 8/9 0.025 ± 0.014 0.028 0.007-0.042

India 37/38 0.018 ± 0.009 0.018 0.003-0.046

Egypt 3/5 0.004 ± 0.001 0.004 0.003-0.005

Surinam 1/1 0.008

Australia 0/1 <LOQ

France 1/1 0.013

USA 6/9 0.041 ± 0.030 0.034 0.014-0.098

Thailand 4/6 0.019 ± 0.007 0.019 0.012-0.028

Pakistan 4/9 0.020 ± 0.002 0.020 0.018-0.022

India 22/38 0.031 ± 0.044 0.018 0.003-0.218

Egypt 3/5 0.021 ± 0.008 0.017 0.015-0.031

Surinam 1/1 0.018

Australia 0/1 <LOQ

France 0/1 <LOQ

a n is the number of samples with concentrations >LOQ out of the total number of samples from the specified country of origin.

Arsenic finds its way to rice grains from As-contaminated soil or As-laden irrigation water or both (Mondal and Polya, 2008; Zavala et al., 2008; Zhu et al., 2008; Khan et al., 2009; Taskeen et al., 2009; Bhattacharya et al., 2010a,b, Rahman et al., 2010). For instance, an investigation by Khan et al. reported an increased pattern of As concentrations in rice grains with an increase in As concentration in the irrigation water, soil, or both (Khan et al., 2009).

In addition to As, rice samples investigated in this work were found to contain variable levels of toxicologically relevant elements such as Ni, Cd, and Pb as shown in Tables 3 and 4. The source of these toxic metals can be anthropogenic, natural, or both (Qian et al., 2010; Lei et al., 2011).

Nickel is one of many metals that are known to cause cancer and many other health complications to humans (Denkhaus and Salnikow, 2002; Henderson et al., 2012). Luckily, almost all of the KSA samples (93%) contained no detectable Ni, while the rest of the samples (n = 5) contained low Ni concentrations with a mean of 0.064 mg kg-1, SD 0.021 mg kg-1, median 0.063 mg kg-1, and range 0.042-0.086 mg kg-1. In comparison, elevated levels of Ni were detected in the Brisbane samples (n = 12) with a mean of 1.83 mg kg-1, SD 0.402 g kg-1, median 1.69 mg kg-1, and range 1.54-3.01 mg kg-1.

Low levels of cadmium were also detected in all the rice samples but none has exceeded the Chinese MCL for Cd (i.e. 0.2 mg kg-1). The mean Cd concentration in the KSA samples was 0.017 mg kg-1 (n = 64, SD 0.010 mg kg-1, range 0.0030.046 mg kg-1), whereas the mean Cd level in the Brisbane samples was 0.039 mg kg-1 (n = 12, SD 0.043 mg kg-1, range

0.002-0.150 mg kg-1). The highest Cd concentration of 0.150 mg kg-1 was recorded for one of the Thailand samples. Similar to arsenic, cadmium has been classified by IARC as a human carcinogen and exposure to high levels of Cd severely irritates the digestive system, causes vomiting and diarrhea, and damages the lungs (Jarup et al., 1998; Nawrot et al., 2006; Akesson, 2011; Lee et al., 2011).

More than half of the KSA samples contained detectable concentrations of lead (i.e. 40 out of 70 samples), but the concentrations are low in most samples. The mean Pb concentration in the samples was 0.029 mg kg-1 (SD 0.039 mg kg-1, median 0.020 mg kg-1, and range 0.003-0.218 mg kg-1). Only one sample of Indian origin contained Pb concentration (0.218 mg kg-1) in excess of Chinese MCL (i.e. 0.2mgkg-1). On the other hand, all the Brisbane samples contained detectable levels of Pb with a mean concentration of 0.120 mg kg-1 (SD 0.133 mg kg-1, median 0.047 mg kg-1, and range 0.0160.354 mg kg-1). Four of the samples contained elevated levels of Pb (0.236-0.354 mg kg-1) in excess of the Chinese MCL.

Due to the widespread contamination of As in groundwater worldwide, most of the investigations that dealt with contamination of rice have concentrated on this metalloid with much less attention focused on other toxic elements that have the tendency to accumulate in rice grains. In one of these few articles that addressed this issue, a survey of the concentrations of some toxic elements such as Cd, Pb, Hg, and As in Chinese rice was carried out between 2005 and 2008, the mean concentration reported for Cd was 0.05 mg kg-1; Pb 0.062 mg kg-1; Hg 0.0058 mg kg-1; and As 0.119 mg kg-1 (Qian et al.,

2010). In another investigation, the reported levels of Cd, Pb, and As in different types of rice samples collected from Swedish retail market were 0.20 mg kg-1 for As, 0.024 mg kg-1 for Cd, and 0.004 mg kg-1for Pb (Jorhem et al., 2008). Elevated levels of Co and Ni have been also reported for rice grains grown on treated soils in India (means for Co and Ni were 0.49, and 0.48 mg kg-1, respectively) (Bhattacharyya et al., 2008). Rice-based baby food was also found to contain high levels of some toxic metals as shown by a Pakistani investigation, where reported concentration ranges (mgkg-1) for Al, Cd, Ni, and Pb were 4.77-35.20, 0.0256-0.883, 0.124-0.332 and 0.053-0.091, respectively (Kazi et al., 2010).

3.3. Concentrations of essential elements in rice samples

Despite its ability to accumulate some toxic elements, rice is known to be a good source of some essential elements to the human body including Fe, Mg, Zn, Cu, Cr, Co, Mn, and Se. The essentiality vs. toxicity of such elements was discussed in the introduction section above.

The concentrations of Fe, Mg, Zn, Cu, Cr, Co, Mn, and Se plus other elements in the rice samples are listed in Table 3.

The mean Fe concentration in KSA samples was 7.07 mg kg-1 (n = 70, SD 8.11 mg kg-1, median 5.53 mg kg-1, and range 1.95-55.1 mg kg-1). A lower mean Fe concentration was found for the Brisbane samples (mean 3.64mgkg-1, SD

I.17 mgkg-1, range 1.75-6.47 mg kg-1, n = 12). This difference may be due to variation in the source.

Magnesium concentrations are the highest among the rice samples followed by Fe, Zn, and Mn. All the samples contained Mg with a mean concentration of 157 mgkg-1 (SD 111 mg kg-1, median 139 mgkg-1, and range 51.8-777 mg kg-1). Two of the Indian rice (brown) contained high Mg levels of 777 and 732 mg kg-1. The mean Mg concentration in the Brisbane samples was 123 mg kg-1 (range 63.7-216 mg kg-1).

Zinc concentrations in Brisbane samples (mean

II.4 mgkg-1, SD 2.6 mgkg-1, and range 8.44-18.3 mg kg-1) were relatively higher that those found in KSA samples (mean 6.19 mg kg-1, SD 3.21 mg kg-1, and range 1.15-13.5 mg kg-1). This variation is also a result of variation in the source.

The mean Mn concentration in the KSA samples was 4.28 mgkg-1 (n = 70, SD 2.17 mgkg-1, range 0.9610.9 mg kg-1) whereas the mean Mn concentration for the Brisbane samples was 9.48 mg kg-1 (n = 12, SD 2.88 mg kg-1, range 6.13-14.8 mg kg-1).

The mean Se concentration in the KSA samples was 0.202mgkg-1 (n = 70, SD 0.133 mgkg-1, median 0.174mg kg-1, and range 0.007-0.574 mg kg-1), whereas the mean Se concentration for the Brisbane samples was 0.041 mg kg-1 (n = 12, SD 0.017 mg kg-1, range 0.028-0.079 mg kg-1).

The mean Cu concentration in the KSA samples was 1.28 mgkg-1 (n = 70, SD 0.339 mgkg-1, and range 0.5082.41 mg kg-1) whereas the mean concentration in the Brisbane samples was 2.72 mg kg-1 (n = 12, SD 1.61 mgkg-1, and range 1.27-6.23 mg kg-1).

Total Cr concentrations in most of the KSA rice samples (73%) were below the LOQ and the mean total Cr concentration in the rest of the samples (n = 19) was 0.057 mg kg-1 (SD 0.045 mgkg-1, median 0.048 mg kg-1, and range 0.0100.184 mg kg-1). Two of these samples; one of USA origin and the other of Indian origin contained relatively elevated

levels of Cr (i.e. 0.144 and 0.184 mg kg 1, respective) but lower than the Chinese MCL for Cr (i.e. 0.2mgkg-1). As for the samples that were collected from Brisbane markets (n = 12), all were found to contain Cr concentration >LOQ with a mean of 0.097 mgkg-1 (SD 0.096 mgkg-1, median 0.070 mgkg-1, and range 0.033-0.390 mg kg-1). Elevated Cr levels in excess of the Chinese MCL for Cr were found in one of the Chinese samples (0.390 mg kg-1).

Finally, Co was found in 80% of the KSA samples with a mean concentration of 0.012 mgkg-1, SD 0.020 mgkg-1, median 0.007 mgkg-1, and range of 0.001-0.116 mg kg-1. Similarly low Co concentrations were found in the Brisbane samples (Table 3).

Different rice grain cultivars have been shown to accumulate variable levels of nutritional elements as reported in the literature. For example the Fe and Zn contents of some Taiwanese rice cultivars ranged from 3.90 to 28.1 mg kg-1 for Fe and 26.2 to 29.0 mg kg-1 for Zn (Jeng et al., 2012). In another investigation, the mean concentrations of Mg, Mn, and Zn in Thai white jasmine rice were 40.5 ± 4.9, 7.3 ± 0.9, and 21.8 ± 4.7 mg kg-1, respectively (Parengam et al., 2010). Concentrations of minerals similar to those reported in this investigation have been stated for 25 rice brands collected from Jamaican markets. The reported mean values (in mg kg-1) for both white and brown rice, respectively were 0.08 and 0.157 for Cr, 1.65 and 2.96 for Cu, 22.3 and 20.1 for Fe, 371 and 1205 for Mg, 10.5 and 26.5 for Mn, 0.108 and 0.131 for Se, and 15.6 and 20.2 for Zn (Antoine et al., 2012).

4. Conclusions

The results of this investigation indicate that some rice varieties sold in the local markets of Almadinah Almunawarah, KSA contain hazardous levels of one or more of the toxic element (e.g. arsenic, chromium, and lead). Additionally, variation in the country of origin of rice resulted in large variation in concentration of both the toxic and essential elements in rice grains. In order to reduce the exposure of the local populations to toxic elements through rice consumption, the concerned authorities are strongly recommended to periodically monitor the levels of toxicologically relevant elements (e.g. arsenic, cadmium, chromium, and lead) in imported rice.

Acknowledgments

This research was funded by the Deanship of Scientific Research - Taibah University (Project No. 432-107). The National Research Centre for Environmental Toxicology (EnTox) is a joint venture of the University of Queensland and Queensland Health.

References

Ahamed, S., Sengupta, M.K., Mukherjee, A., Hossain, M.A., Das, B., Nayak, B., Pal, A., Mukhejee, S.C., Pati, S., Dutta, R.N., Chattejee, G., Mukhejee, A., Srivastava, R., Chakraborti, D., 2006. Arsenic groundwater contamination and its health effects in the state of Uttar Pradesh (UP) in upper and middle Ganga plain, India: a severe danger. Sci. Total Environ. 370 (2-3), 310-322.

Akesson, A. 2011. Cadmium Exposure in the Environment: Renal Effects and the Benchmark Dose. Encyclopedia of Environmental Health. O. N. Editor-in-Chief: Jerome. Burlington, Elsevier: 465473.

Antoine, J.M.R., Hoo Fung, L.A., Grant, C.N., Dennis, H.T., Lalor, G.C., 2012. Dietary intake of minerals and trace elements in rice on the Jamaican market. J Food Compos. Anal. 26 (1-2), 111-121.

Batista, B.L., Souza, J.M.O., De Souza, S.S., Barbosa Jr., F., 2011. Speciation of arsenic in rice and estimation of daily intake of different arsenic species by Brazilians through rice consumption. J. Hazard. Mater. 191 (1-3), 342-348.

Bhattacharya, P., Samal, A.C., Majumdar, J., Santra, S.C., 2010a. Accumulation of arsenic and its distribution in rice plant (Oryza sativa L.) in Gangetic West Bengal, India. Paddy Water Environ. 8 (1), 63-70.

Bhattacharya, P., Samal, A.C., Majumdar, J., Santra, S.C., 2010b. Arsenic contamination in rice, wheat, pulses, and vegetables: a study in an arsenic affected area of West Bengal India. Water Air Soil Pollut. 213 (1-4), 3-13.

Bhattacharyya, P., Chakrabarti, K., Chakraborty, A., Tripathy, S., Kim, K., Powell, M.A., 2008. Cobalt and nickel uptake by rice and accumulation in soil amended with municipal solid waste compost. Ecotoxicol. Environ. Saf. 69 (3), 506-512.

Blust, R. 2011. 6 - Cobalt. Fish Physiology. A. P. F. Chris M. Wood, J. B. Colin, Academic Press. Vol. 31, Part A: 291-326.

Booth, B., 2009. Cancer rates attributable to arsenic in rice vary globally. Environ. Sci. Technol. 43 (5), 1243-1244.

Broadley, M., Brown, P., Cakmak, I., Ma, J. F., Rengel, Z., Zhao, F. 2012. Chapter 8 - Beneficial Elements. Marschner's Mineral Nutrition of Higher Plants (Third Ed.). M. Petra. San Diego, Academic Press: 249-269.

Cantor, K.P., Ward, M.H., Scanlan, L.P., Slattery, M. 2000. Arsenic in drinking water and bladder cancer: a case-control study in Utah, USA. Interdisciplinary Perspectives on Drinking Water Risk Assessment and Management. E. G. Reichard, F. S. Hauchman, A. M. Sancha: 27-27.

Celik, I., Gallicchio, L., Boyd, K., Lam, T.K., Matanoski, G., Tao, X.G., Shiels, M., Hammond, E., Chen, L., Robinson, K.A., Caulfield, L.E., Herman, J.G., Guallar, E., Alberg, A.J., 2008. Arsenic in drinking water and lung cancer: a systematic review. Environ. Res. 108 (1), 48-55.

Denkhaus, E., Salnikow, K., 2002. Nickel essentiality, toxicity, and carcinogenicity. Crit. Rev. Oncol./Hematol. 42 (1), 35-56.

FAO 2010. Food Outlook: Global Market Analysis. Date accessed: 30/01/2014, http://www.fao.org/docrep/012/ak349e/ak349e00.pdf.

Fewtrell, L.J., Pruss-Ustun, A., Landrigan, P., Ayuso-Mateos, J.L., 2004. Estimating the global burden of disease of mild mental retardation and cardiovascular diseases from environmental lead exposure. Environ. Res. 94 (2), 120-133.

Fraga, C.G., 2005. Relevance, essentiality and toxicity of trace elements in human health. Mol. Aspects of Med. 26 (4-5), 235-244.

Fu, Y., Chen, M., Bi, X., He, Y., Ren, L., Xiang, W., Qiao, S., Yan, S., Li, Z., Ma, Z., 2011. Occurrence of arsenic in brown rice and its relationship to soil properties from Hainan Island China. Environ. Pollut. 159 (7), 1757-1762.

Goldhaber, S.B., 2003. Trace element risk assessment: essentiality vs. toxicity. Regul. Toxicol. Pharmacol. 38 (2), 232-242.

Guo, H. R., Chiang, H. S., Hu, H., Lipsitz, S. R. and Monson, R. R. 1997. Arsenic in drinking water and incidence of urinary cancers. Epidemiology (Cambridge, Mass.) 8(5): 545-550.

Guo, X.J., Fujino, Y., Kaneko, S., Wu, K.G., Xia, Y.J., Yoshimura, T., 2001. Arsenic contamination of groundwater and prevalence of arsenical dermatosis in the Hetao plain area, Inner Mongolia China. Mol. Cell. Biochem. 222 (1-2), 137-140.

Harrison, R.M. (Ed.), 2001. Pollution: Causes, Effects and Control. The Royal Society of Chemistry, Cambridge.

Henderson, R.G., Durando, J., Oller, A.R., Merkel, D.J., Marone, P.A., Bates, H.K., 2012. Acute oral toxicity of nickel compounds. Regul. Toxicol. Pharmacol. 62 (3), 425-432.

Hirano, S., Kobayashi, Y., Cui, X., Kanno, S., Hayakawa, T., Shraim, A., 2004. The accumulation and toxicity of methylated arsenicals in endothelial cells: important roles of thiol compounds. Toxicol. Appl. Pharmacol. 198 (3), 458-467.

Hughes, M.F., 2002. Arsenic toxicity and potential mechanisms of action. Toxicol. Lett. 133 (1), 1-16.

IARC 1987. IARC monographs on the evaluation of the carcinogenic risks to humans: Arsenic and arsenic compounds. Report number: 23, Suppl. 7.

Jarup, L., 2003. Hazards of heavy metal contamination. Br. Med. Bull. 68 (1), 167-182.

Jarup, L., Berglund, M., Elinder, C.G., Nordberg, G., Vahter, M., 1998. Health effects of cadmium exposure - a review of the literature and a risk estimate. Scandinavian Journal of Work Environment & Health (vol 24, pg 1, 1998), 24(3): 240-240.

Jeng, T.L., Lin, Y.W., Wang, C.S., Sung, J.M., 2012. Comparisons and selection of rice mutants with high iron and zinc contents in their polished grains that were mutated from the indica type cultivar IR64. J. Food Compos. Anal. 28 (2), 149-154.

Jorhem, L., Astrand, C., Sundstrom, B., Baxter, M., Stokes, P., Lewis, J., Grawe, K.P., 2008. Elements in rice from the Swedish market: 1. Cadmium, lead and arsenic (total and inorganic). Food Addit. Contam. 25 (3), 284-292.

Juhasz, A.L., Smith, E., Weber, J., Rees, M., Rofe, A., Kuchel, T., Sansom, L., Naidu, R., 2006. In vivo assessment of arsenic bioavailability in rice and its significance for human health risk assessment. Environ. Health Perspect. 114 (12), 1826-1831.

Kanel, S. R., Choi, H., Kim, K. W. and Moon, S. H. 2005. Arsenic contamination in groundwater in Nepal: a new perspective and more health threat in South Asia.

Karagas, M.R., 2001. Arsenic and skin cancer in the USA. Epidemiology 12 (4), pp. S28-S28.

Kazi, T.G., Jalbani, N., Baig, J.A., Arain, M.B., Afridi, H.I., Jamali, M.K., Shah, A.Q., Memon, A.N., 2010. Evaluation of toxic elements in baby foods commercially available in Pakistan. Food Chem. 119 (4), 1313-1317.

Khan, M.A., Islam, M.R., Panaullah, G.M., Duxbury, J.M., Jahirud-din, M., Loeppert, R.H., 2009. Fate of irrigation-water arsenic in rice soils of Bangladesh. Plant Soil 322 (1-2), 263-277.

Khan, M.A., Islam, M.R., Panaullah, G.M., Duxbury, J.M., Jahirud-din, M., Loeppert, R.H., 2010. Accumulation of arsenic in soil and rice under wetland condition in Bangladesh. Plant Soil 333 (1-2), 263-274.

Khan, F.H., Ambreen, K., Fatima, G., Kumar, S., 2012. Assessment of health risks with reference to oxidative stress and DNA damage in chromium exposed population. Sci. Total Environ. 430, 68-74.

Kuramata, M., Abe, T., Matsumoto, S., Ishikawa, S., 2011. Arsenic accumulation and speciation in Japanese paddy rice cultivars. Soil Sci. Plant Nutr. 57 (2), 248-258.

Lamb, M.R., Janevic, T., Liu, X., Cooper, T., Kline, J., Factor-Litvak, P., 2008. Environmental lead exposure, maternal thyroid function, and childhood growth. Environ. Res. 106 (2), 195-202.

Lee, M.-S., Park, S.K., Hu, H., Lee, S., 2011. Cadmium exposure and cardiovascular disease in the 2005 Korea National Health and Nutrition Examination Survey. Environ. Res. 111 (1), 171-176.

Lei, M., Tie, B.Q., Williams, P.N., Zheng, Y.M., Huang, Y.Z., 2011. Arsenic, cadmium, and lead pollution and uptake by rice (Oryza sativa L.) grown in greenhouse. J. Soils Sed. 11 (1), 115-123.

Liang, F., Li, Y.L., Zhang, G.L., Tan, M.G., Lin, J., Liu, W., Li, Y., Lu, W.W., 2010. Total and speciated arsenic levels in rice from China. Food Addit. Contam. Part a-Chem. Anal. Control Expo. Risk Assess. 27 (6), 810-816.

Meharg, A.A., Sun, G., Williams, P.N., Adomako, E., Deacon, C., Zhu, Y.-G., Feldmann, J., Raab, A., 2008. Inorganic arsenic levels in baby rice are of concern. Environ. Pollut. 152 (3), 746-749.

Meharg, A.A., Williams, P.N., Adomako, E., Lawgali, Y.Y., Deacon, C., Villada, A., Cambell, R.C.J., Sun, G., Zhu, Y.G., Feldmann, J., Raab, A., Zhao, F.J., Islam, R., Hossain, S., Yanai, J., 2009. Geographical Variation in Total and Inorganic Arsenic Content of Polished (White) Rice. Environ. Sci. Technol. 43 (5), 1612-1617.

Ministry of Health, P. R. O. C. 2012. National Food Safety Standard: Maximum Levels of Contaminants in Foods. Report number: GB 2762-2012.

Mondal, D., Polya, D.A., 2008. Rice is a major exposure route for arsenic in Chakdaha block, Nadia district, West Bengal, India: a probabilistic risk assessment. Appl. Geochem. 23 (11), 2987-2998.

Navarro-Alarcon, M., Lopez-Martinez, M.C., 2000. Essentiality of selenium in the human body: relationship with different diseases. Sci. Total Environ. 249 (1-3), 347-371.

Nawrot, T., Plusquin, M., Hogervorst, J., Roels, H.A., Celis, H., Thijs, L., Vangronsveld, J., Van Hecke, E., Staessen, J.A., 2006. Environmental exposure to cadmium and risk of cancer: a prospective population-based study. Lancet Oncol. 7 (2), 119-126.

Neumann, R.B., St Vincent, A.P., Roberts, L.C., Badruzzaman, A.B.M., Ali, M.A., Harvey, C.F., 2011. Rice field geochemistry and hydrology: an explanation for why groundwater irrigated fields in Bangladesh are net sinks of arsenic from groundwater. Environ. Sci. Technol. 45 (6), 2072-2078.

Ng, J. C., Seawright, A. A., Qi, L., Garnett, C. M., Chiswell, B. and Moore, M. R. 1999. Tumors in mice induced by exposure to sodium arsenate in drinking water. Arsenic Exposure and Health Effects. W. R. Chappell, C. O. Abernathy and R. L. Calderon, Alsevier: 217-223.

Ng, J.C., Wang, J., Shraim, A., 2003. A global health problem caused by arsenic from natural sources; a review. Chemosphere 52 (9), 1353-1359.

Nickens, K.P., Patierno, S.R., Ceryak, S., 2010. Chromium genotox-icity: a double-edged sword. Chem. Biol. Interact. 188 (2), 276-288.

Nickson, R.T., McArthur, J.M., Shrestha, B., Kyaw-Myint, T.O., Lowry, D., 2005. Arsenic and other drinking water quality issues, Muzaffargarh District Pakistan. Appl. Geochem. 20 (1), 55-68.

Nielsen, F.H., 2007. Chapter 13 - Summary: The clinical and nutritional importance of chromium -- still debated after 50 years of research. Nutritional Biochemistry of Chromium (III). Elsevier, Amsterdam, pp. 265-276.

Nriagu, J.O., 1992. Toxic metal pollution in Africa. Sci. Total Environ. 121, 1-37.

Parengam, M., Judprasong, K., Srianujata, S., Jittinandana, S., Laoharojanaphand, S., Busamongko, A., 2010. Study of nutrients and toxic minerals in rice and legumes by instrumental neutron activation analysis and graphite furnace atomic absorption spec-trophotometry. J. Food Compos. Anal. 23 (4), 340-345.

Qian, Y., Chen, C., Zhang, Q., Li, Y., Chen, Z., Li, M., 2010. Concentrations of cadmium, lead, mercury and arsenic in Chinese market milled rice and associated population health risk. Food Control 21, 1757-1763 (12, Supplement).

Rahman, M.A., Hasegawa, H., 2011. Review. High levels of inorganic arsenic in rice in areas where arsenic-contaminated water is used for irrigation and cooking. Sci. Total Environ. 409 (22), 4645-4655.

Rahman, M.M., Naidu, R., Bhattacharya, P., 2009. Arsenic contamination in groundwater in the Southeast Asia region. Environ. Geochem. Health 31, 9-21.

Rahman, M.S., Miah, M.A.M., Khaled, H.M., Islam, A., Panaullah, G.M., 2010. Arsenic concentrations in groundwater, soils, and

irrigated rice in Southwestern Bangladesh. Commun. Soil Sci. Plant Anal. 41 (16), 1889-1895.

Sato, H., Murai, K., Kanda, T., Mimura, R., Hiratsuka, Y., 2003. Association of chromium exposure with multiple primary cancers in the nasal cavity. Auris Nasus Larynx 30 (1), 93-96.

Shiber, J., 2007. Arsenic in Central Appalachian (USA) domestic well water and human health.

Shinkai, Y., Van Truc, D., Sumi, D., Canh, D., Kumagai, Y., 2007. Arsenic and other metal contamination of groundwater in the Mekong River Delta Vietnam. J. Health Sci. 53 (3), 344-346.

Shraim, A., Cui, X., Li, S., Ng, J.C., Wang, J., Jin, Y., Liu, Y., Guo, L., Li, D., Wang, S., Zhang, R., Hirano, S., 2003. Arsenic speciation in the urine and hair of individuals exposed to airborne arsenic through coal-burning in Guizhou, PR China. Toxicol. Lett. 137, 35-48.

Shrestha, R.R., Shrestha, M.P., Upadhyay, N.P., Pradhan, R., Khadka, R., Maskey, A., Maharjan, M., Tuladhar, S., Dahal, B.M., Shrestha, K., 2003. Groundwater arsenic contamination, its health impact and mitigation program in Nepal. J. Environ. Sci. Health Part a-Toxic/Hazard. Subst. Environ. Eng. 38 (1), 185-200.

Singh, V., Brar, M.S., Sharma, P., Malhi, S.S., 2010. Arsenic in water, soil, and rice plants in the Indo-Gangetic Plains of Northwestern India. Commun. Soil Sci. Plant Anal. 41 (11), 1350-1360.

Smith, N.M., Lee, R., Heitkemper, D.T., Cafferky, K.D., Haque, A., Henderson, A.K., 2006. Inorganic arsenic in cooked rice and vegetables from Bangladeshi households. Sci. Total Environ. 370 (2-3), 294-301.

Stanley Manahan, E., 2000. Environmental Chemistry. CRC Press LLC, Boca Raton.

Takahashi, Y., Minamikawa, R., Hattori, K.H., Kurishima, K., Kihou, N., Yuita, K., 2004. Arsenic behavior in paddy fields during the cycle of flooded and non-flooded periods. Environ. Sci. Technol. 38 (4), 1038-1044.

Taskeen, A., Naeem, I., Siddique, Z., 2009. Public health risk of arsenic contamination in food at Old Kahna, Lahore Pakistan. Asian J. Chem. 21 (4), 2845-2848.

van Geen, A., Zheng, Y., Cheng, Z., He, Y., Dhar, R.K., Garnier, J.M., Rose, J., Seddique, A., Hoque, M.A., Ahmed, K.M., 2006. Impact of irrigating rice paddies with groundwater containing arsenic in Bangladesh. Sci. Total Environ. 367 (2-3), 769-777.

Wailes, E. J. 2005. Rice: Global Trade, Proptectioist Policies, and the Impact of Trade Liberalization. Global Agricultural Trade and Developing Countries. M. A. Aksoy and J. C. Beghin. Washington, D.C., The World Bank.

World Health Organization 2001. Environmental Health Criteria 224: Arsenic and Arsenic Compounds. Report number: Environmental Health Criteria 224.

Xie, X., Ding, G., Cui, C., Chen, L., Gao, Y., Zhou, Y., Shi, R., Tian, Y., 2013. The effects of low-level prenatal lead exposure on birth outcomes. Environ. Pollut. 175, 30-34.

Zavala, Y.J., Duxbury, J.M., 2008. Arsenic in rice: I. Estimating normal levels of total arsenic in rice grain. Environ. Sci. Technol. 42 (10), 3856-3860.

Zavala, Y.J., Gerads, R., Gurleyuk, H., Duxbury, J.M., 2008. Arsenic in rice: II. Arsenic speciation in USA grain and implications for human health. Environ. Sci. Technol. 42 (10), 3861-3866.

Zhu, Y.-G., Williams, P.N., Meharg, A.A., 2008. Exposure to inorganic arsenic from rice: a global health issue? Environ. Pollut. 154 (2), 169-171.