Arsenic contamination of Bangladesh paddy field soils: implications for rice contribution to arsenic consumption

Arsenic contaminated groundwater is used extensively in Bangladesh to irrigate the staple food of the region, paddy rice (Oryza sativa L.). To determine if this irrigation has led to a buildup of arsenic levels in paddy fields, and the consequences for arsenic exposure through rice ingestion, a survey of arsenic levels in paddy soils and rice grain was undertaken. Survey of paddy soils throughout Bangladesh showed that arsenic levels were elevated in zones where arsenic in groundwater used for irrigation was high, and where these tube-wells have been in operation for the longest period of time. Regression of soil arsenic levels with tube-well age was significant. Arsenic levels reached 46 microg g(-1) dry weight in the most affected zone, compared to levels below l0 microg g(-1) in areas with low levels of arsenic in the groundwater. Arsenic levels in rice grain from an area of Bangladesh with low levels of arsenic in groundwaters and in paddy soils showed that levels were typical of other regions of the world. Modeling determined, even these typical grain arsenic levels contributed considerably to arsenic ingestion when drinking water contained the elevated quantity of 0.1 mg L(-1). Arsenic levels in rice can be further elevated in rice growing on arsenic contaminated soils, potentially greatly increasing arsenic exposure of the Bangladesh population. Rice grain grown in the regions where arsenic is building up in the soil had high arsenic concentrations, with three rice grain samples having levels above 1.7 microg g(-1).     

Arsenic bioavailability to rice is elevated in Bangladeshi paddy soils

Some paddy soils in the Bengal delta are contaminated with arsenic (As) due to irrigation of As-laden groundwater, which may lead to yield losses and elevated As transfer to the food chain. Whether these soils have a higher As bioavailability than other soils containing either geogenic As or contaminated by mining activities was investigated in a pot experiment. Fourteen soils varying in the source and the degree (4-138 mg As kg 1?1) of As contamination were collected, 10 from Bangladeshi paddy fields (contaminated by irrigation water) and two each from China and the UK (geogenic or mining impacted), for comparison. Bangladeshi soils had higher percentages of the total As extractable by ammonium phosphate (specifically sorbed As) than other soils and also released more As into the porewater upon flooding. Porewater As concentrations increased with increasing soil As concentrations more steeply in Bangladeshi soils, with arsenite being the dominant As species. Rice growth and grain yield decreased markedly in Bangladeshi soils containing > 13 mg As kg 1?1, but not in the other soils. Phosphate-extractable or porewater As was a better indicator of As bioavailability than total soil As. Rice straw As concentrations increased with increasing soil As concentrations; however, As phytotoxicity appeared to result in lower grain As concentrations. The relative proportions of inorganic As and dimethylarsinic acid (DMA) in grain varied among soils, and the percentage DMA was larger in greenhouse-grown plants than grain samples collected from the paddy fields of the same soil and the same rice cultivar, indicating a strong environmental influence on As species found in rice grain. This study shows that Bangladeshi paddy soils contaminated by irrigation had a higher As bioavailability than other soils, resulting in As phytotoxicity in rice and substantial yield losses.     

Spatial distribution and temporal variability of arsenic in irrigated rice fields in Bangladesh. 2. Paddy soil

Arsenic-rich groundwater from shallow tube wells is widely used for the irrigation of boro rice in Bangladesh and West Bengal. In the long term this may lead to the accumulation of As in paddy soils and potentially have adverse effects on rice yield and quality. In the companion article in this issue, we have shown that As input into paddy fields with irrigation water is laterally heterogeneous. To assess the potential for As accumulation in soil, we investigated the lateral and vertical distribution of As in rice field soils near Sreenagar (Munshiganj, Bangladesh) and its changes over a 1 year cycle of irrigation and monsoon flooding. At the study site, 18 paddy fields are irrigated with water from a shallow tube well containing 397 +/- 7 microg L(-1) As. The analysis of soil samples collected before irrigation in December 2004 showed that soil As concentrations in paddy fields did not depend on the length of the irrigation channel between well and field inlet. Within individual fields, however, soil As contents decreased with increasing distance to the water inlet, leading to highly variable topsoil As contents (11-35 mg kg(-1), 0-10 cm). Soil As contents after irrigation (May 2005) showed that most As input occurred close to the water inlet and that most As was retained in the top few centimeters of soil. After monsoon flooding (December 2005), topsoil As contents were again close to levels measured before irrigation. Thus, As input during irrigation was at least partly counteracted by As mobilization during monsoon flooding. However, the persisting lateral As distribution suggests net arsenic accumulation over the past 15 years. More pronounced As accumulation may occur in regions with several rice crops per year, less intense monsoon flooding, or different irrigation schemes. The high lateral and vertical heterogeneity of soil As contents must be taken into account in future studies related to As accumulation in paddy soils and potential As transfer into rice.     

Arsenic in soil and irrigation water affects arsenic uptake by rice: complementary insights from field and pot studies

Groundwater rich in arsenic (As) is extensively used for dry season boro rice cultivation in Bangladesh, leading to long-term As accumulation in soils. This may result in increasing levels of As in rice straw and grain, and eventually, in decreasing rice yields due to As phytotoxicity. In this study, we investigated the As contents of rice straw and grain over three consecutive harvest seasons (2005-2007) in a paddy field in Munshiganj, Bangladesh, which exhibits a documented gradient in soil As caused by annual irrigation with As-rich groundwater since the early 1990s. The field data revealed that straw and grain As concentrations were elevated in the field and highest near the irrigation water inlet, where As concentrations in both soil and irrigation water were highest. Additionally, a pot experiment with soils and rice seeds from the field site was carried out in which soil and irrigation water As were varied in a full factorial design. The results suggested that both soil As accumulated in previous years and As freshly introduced with irrigation water influence As uptake during rice growth. At similar soil As contents, plants grown in pots exhibited similar grain and straw As contents as plants grown in the field. This suggested that the results from pot experiments performed at higher soil As levels can be used to assess the effect of continuing soil As accumulation on As content and yield of rice. On the basis of a recently published scenario of long-term As accumulation at the study site, we estimate that, under unchanged irrigation practice, average grain As concentrations will increase from currently ～0.15 mg As kg(-1) to 0.25-0.58 mg As kg(-1) by the year 2050. This translates to a 1.5-3.8 times higher As intake by the local population via rice, possibly exceeding the provisional tolerable As intake value defined by FAO/WHO.     

Variation in arsenic speciation and concentration in paddy rice related to dietary exposure

Ingestion of drinking water is not the only elevated source of arsenic to the diet in the Bengal Delta. Even at background levels, the arsenic in rice contributes considerably to arsenic ingestion in subsistence rice diets. We set out to survey As speciation in different rice varieties from different parts of the globe to understand the contribution of rice to arsenic exposure. Pot experiments were utilized to ascertain whether growing rice on As contaminated soil affected speciation and whether genetic variation accounted for uptake and speciation. USA long grain rice had the highest mean arsenic level in the grain at 0.26 microg As g(-1) (n = 7), and the highest grain arsenic value of the survey at 0.40 microg As g(-1). The mean arsenic level of Bangladeshi rice was 0.13 microg As g(-1) (n = 15). The main As species detected in the rice extract were AsIII, DMAV, and AsV. In European, Bangladeshi, and Indian rice 64 +/- 1% (n = 7), 80 +/- 3% (n = 11), and 81 +/- 4% (n = 15), respectively, of the recovered arsenic was found to be inorganic. In contrast, DMAV was the predominant species in rice from the USA, with only 42 +/- 5% (n = 12) of the arsenic being inorganic. Pot experiments show that the proportions of DMAV in the grain are significantly dependent on rice cultivar (p = 0.026) and that plant nutrient status is effected by arsenic exposure.     

Market basket survey shows elevated levels of As in South Central U.S. processed rice compared to California: consequences for human dietary exposure

We report the largest market basket survey of arsenic (As) in U.S. rice to date. Our findings show differences in transitional-metal levels between polished and unpolished rice and geographical variation in As and selenium (Se) between rice processed in California and the South Central U.S. The mean and median As grain levels for the South Central U.S. were 0.30 and 0.27 mimcrog As g(-1), respectively, for 107 samples. Levels for California were 41% lower than the South Central U.S., with a mean of 0.17 microg As g(-1) and a median of 0.16 microg As g(-1) for 27 samples. The mean and median Se grain levels for the South Central U.S. were 0.19 microg Se g(-1). Californian rice levels were lower, averaging only 0.08 and 0.06 microg Se g(-1) for mean and median values, respectively. The difference between the two regions was found to be significant for As and Se (General Linear Model (GLM): As p < 0.001; Se p < 0.001). No statistically significant differences were observed in As or Se levels between polished and unpolished rice (GLM: As p= 0.213; Se p= 0.113). No significant differences in grain levels of manganese (Mn), cobalt (Co), copper (Cu), or zinc (Zn) were observed between California and the South Central U.S. Modeling arsenic intake for the U.S. population based on this survey shows that for certain groups (namely Hispanics, Asians, sufferers of Celiac disease, and infants) dietary exposure to inorganic As from elevated levels in rice potentially exceeds the maximum intake of As from drinking water (based on consumption of 1 L of 0.01 mg L(-1) In. As) and Californian state exposure limits. Further studies on the transformation of As in soil, grain As bioavailability in the human gastrointestinal tract, and grain elemental speciation trends are critical.     

Arsenic dynamics in porewater of an intermittently irrigated paddy field in Bangladesh

In Bangladesh, irrigation of dry season rice (boro) with arsenic-contaminated groundwater is leading to increased As levels in soils and rice, and to concerns about As-induced yield reduction. Arsenic concentrations and speciation in soil porewater are strongly influenced by redox conditions, and thus by water management during rice growth. We studied the dynamics of As, Fe, P, Si, and other elements in porewater of a paddy field near Sreenagar (Munshiganj), irrigated according to local practice, in which flooding was intermittent. During early rice growth, As porewater concentrations reached up to 500 μg L(-1) and were dominated by As(III), but As release was constrained to the lower portion of the soil above the plow pan. In the later part of the season, soil conditions were oxic throughout the depth range relevant to rice roots and porewater concentrations only intermittently increased to ～150 μg L(-1) As(V) following irrigation events. Our findings suggest that intermittent irrigation, currently advocated in Bangladesh for water-saving purposes, may be a promising means of reducing As input to paddy soils and rice plant exposure to As.     

Assessing the labile arsenic pool in contaminated paddy soils by isotopic dilution techniques and simple extractions

Arsenic (As) contamination of paddy soils threatens rice cultivation and the health of populations relying on rice as a staple crop. In the present study, isotopic dilution techniques were used to determine the chemically labile (E value) and phytoavailable (L value) pools of As in a range of paddy soils from Bangladesh, India, and China and two arable soils from the UK varying in the degree and sources of As contamination. The E value accounted for 6.2-21.4% of the total As, suggesting that a large proportion of soil As is chemically nonlabile. L values measured with rice grown under anaerobic conditions were generally larger than those under aerobic conditions, indicating increased potentially phytoavailable pool of As in flooded soils. In an incubation study, As was mobilized into soil pore water mainly as arsenite under flooded conditions, with Bangladeshi soils contaminated by irrigation of groundwater showing a greater potential of As mobilization than other soils. Arsenic mobilization was best predicted by phosphate-extractable As in the soils.     

Natural occurrence of scirpentriol in cereals infected by Fusarium species.

Wheat, barley and oat grain samples naturally contaminated with Fusarium spp. were analysed for the presence of scirpentriol (STO). This toxin was detected in 1, 37 and 8% of 248 wheat, 32 barley and 99 oat grain samples, respectively, and the maximum concentration was 83 microg x kg(-1). Samples of wheat and oat grain with visible scab symptoms were also analysed, and STO (mean level 255 microg x kg(-1)) was detected only in oat samples infected with F. sporotrichioides and F. poae as the dominant species. We analysed 15 barley samples that were subdivided based on seed size into fractions of <2.5 and > 2.5 mm in diameter. The smaller kernels contained an average 94% of the STO in the samples (in kernel fraction > 2.5 mm 28 microg x kg(-1), <2.5 mm 297 microg x kg(-1)). In oats, STO levels were highest in the chaff, lower in the stalk's apical internode and lowest in the grain.     

Total and inorganic arsenic concentrations in rice sold in Spain, effect of cooking, and risk assessments

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 microg mL(-1)). In raw rice, inorganic As represented 27-93% of total As: total As = 0.188 +/- 0.078 microg g(-1) dry weight (dw); inorganic As = 0.114 +/- 0.046 microg 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 microg g(-1) dw (0.1 microg mL(-1) in the cooking water) and 3.89 microg g(-1) dw (1.0 microg microL(-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 microg 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.     

Evaluation of S-residues in grains and grain fractions fumigated with S-labelled carbonyl sulfide

³⁵S-labelled carbonyl sulfide (CO³⁵S) was used to measure the amount of sorbed ³⁵S residues and converted ³⁵S residues in grains and grain fractions after fumigation with CO³⁵S. Hard wheat, soft wheat, paddy rice, brown rice, polished rice, sorghum, maize, canola, barley, oats and peas were exposed for 4 days to 50 mg L⁻¹ of CO³⁵S with a total radioactivity of 20 mCi. After exposure, the samples were aired. The levels of ³⁵S residues varied with extraction solvent, e.g. 0.003–0.02 mg (COS equivalents) kg⁻¹ (grain) in chloroform extractions and 0.09–0.38 mg kg⁻¹ in water extractions. More than 90% of ³⁵S (COS equivalents) residues were in the water extractions. The total radioactivity determined by scanning radiation images (fluorescent image) of extractions and sectioned commodities ranged from 0.1 to 0.4 mg kg⁻¹. The radiation image shows that more than 90% of ³⁵S residues were located or distributed in the embryo, testa, pericarp and husk, and that the ³⁵S was still slowly desorbing from grains after 2 days aeration.     

Increase in rice grain arsenic for regions of Bangladesh irrigating paddies with elevated arsenic in groundwaters

Concern has been raised by Bangladeshi and international scientists about elevated levels of arsenic in Bengali food, particularly in rice grain. This is the first inclusive food market-basket survey from Bangladesh, which addresses the speciation and concentration of arsenic in rice, vegetables, pulses, and spices. Three hundred thirty aman and boro rice, 94 vegetables, and 50 pulse and spice samples were analyzed for total arsenic, using inductivity coupled plasma mass spectrometry (ICP-MS). The districts with the highest mean arsenic rice grain levels were all from southwestern Bangladesh: Faridpur (boro) 0.51 > Satkhira (boro) 0.38 > Satkhira (aman) 0.36 > Chuadanga (boro) 0.32 > Meherpur (boro) 0.29 microg As g(-1). The vast majority of food ingested arsenic in Bangladesh diets was found to be inorganic; with the predominant species detected in Bangladesh rice being arsenite (AsIII) or arsenate (AsV) with dimethyl arsinic acid (DMAV) being a minor component. Vegetables, pulses, and spices are less important to total arsenic intake than water and rice. Predicted inorganic arsenic intake from rice is modeled with the equivalent intake from drinking water for a typical Bangladesh diet. Daily consumption of rice with a total arsenic level of 0.08 microg As g(-1) would be equivalent to a drinking water arsenic level of 10 microg L(-1).     

Moniliformin in Norwegian grain.

Norwegian grain samples (73 oats, 75 barley, 83 wheat) from the 2000-02 growing seasons were examined for contamination with moniliformin, and the association between the fungal metabolite and the number of kernels infected with common Fusaria was investigated. Before quantification of moniliformin using ion pairing reversed-phase high-performance liquid chromatography with diode array ultraviolet light detection, all samples were extracted using acetonitrile/water (84/16) and disposable strong anion exchange columns used for clean up. The limit of detection was 40 microg kg(-1). Moniliformin was found in 25, 32 and 76% of the barley, oats and wheat samples, respectively. The maximum concentrations of moniliformin in barley, oats and wheat were 380, 210 and 950 microg kg(-1), respectively. At the same time, the prevalence and infection level of the moniliformin-producing F. avenaceum/arthrosporioides was as high as 100 and >53% on average, respectively. Moniliformin concentrations were significantly correlated to the variables grain species, growing season and infection with F. avenaceum/arthrosporioides and F. culmorum. The survey indicates that the prevalence of moniliformin in Norwegian grain is high, especially in wheat. On the other hand, field conditions in Norway do not seem to favour contamination of grain with high levels of moniliformin.     

High percentage inorganic arsenic content of mining impacted and nonimpacted Chinese rice

Two approaches were undertaken to characterize the arsenic (As) content of Chinese rice. First, a national market basket survey (n = 240) was conducted in provincial capitals, sourcing grain from China's premier rice production areas. Second, to reflect rural diets, paddy rice (n = 195) directly from farmers fields were collected from three regions in Hunan, a key rice producing province located in southern China. Two of the sites were within mining and smeltery districts, and the third was devoid of large-scale metal processing industries. Arsenic levels were determined in all the samples while a subset (n = 33) were characterized for As species, using a new simple and rapid extraction method suitable for use with Hamilton PRP-X100 anion exchange columns and HPLC-ICP-MS. The vast majority (85%) of the market rice grains possessed total As levels < 150 ng g(-1). The rice collected from mine-impacted regions, however, were found to be highly enriched in As, reaching concentrations of up to 624 ng g(-1). Inorganic As (As(i)) was the predominant species detected in all of the speciated grain, with As(i) levels in some samples exceeding 300 ng g(-1). The As(i) concentration in polished and unpolished Chinese rice was successfully predicted from total As levels. The mean baseline concentrations for As(i) in Chinese market rice based on this survey were estimated to be 96 ng g(-1) while levels in mine-impacted areas were higher with ca. 50% of the rice in one region predicted to fail the national standard.     

Growing rice aerobically markedly decreases arsenic accumulation

Arsenic (As) exposure from consumption of rice can be substantial, particularly for the population on a subsistence rice diet in South Asia. Paddy rice has a much enhanced As accumulation compared with other cereal crops, and practical measures are urgently needed to decrease As transfer from soil to grain. We investigated the dynamics of As speciation in the soil solution under both flooded and aerobic conditions and compared As accumulation in rice shoot and grain in a greenhouse experiment. Flooding of soil led to a rapid mobilization of As, mainly as arsenite, in the soil solution. Arsenic concentrations in the soil solution were 7-16 and 4-13 times higher under the flooded than under the aerobic conditions in the control without As addition and in the +As treatments (10 mg As kg(-1) as arsenite or arsenate), respectively. Arsenate was the main As species in the aerobic soil. Arsenic accumulation in rice shoots and grain was markedly increased under flooded conditions; grain As concentrations were 10-15-fold higher in flooded than in aerobically grown rice. With increasing total As concentrations in grain, the proportion of inorganic As decreased, while that of dimethylarsinic acid (DMA) increased. The concentration of inorganic As was 2.6-2.9 fold higher in the grain from the flooded treatment than in that from the aerobic treatment. The results demonstrate that a greatly increased bioavailability of As under the flooded conditions is the main reason for an enhanced As accumulation by flooded rice, and growing rice aerobically can dramatically decrease the As transfer from soil to grain.     

Distribution of aflatoxins in shelling and milling fractions of naturally contaminated rice

The objective of this study was to determine the distribution of an economically important class of mycotoxins, the aflatoxins, in rice milling fractions. Rice plants grown under field production conditions are frequently infected with types of pathogenic fungi that produce toxic metabolites (mycotoxins). Paddy (seeds) rice from healthy plants in the field was collected and stored on a farm under humid, poorly ventilated conditions. Samples were milled into four fractions (hulls, brown rice, bran and white rice) and analysed for aflatoxins (B(1), B(2), G(1) and G(2)) using a validated method. Rice fractions from healthy plants, which contained low levels of aflatoxins (less than 1?μg?kg(-1)), were used to determine the efficiency of the extraction method. Seeds stored under poor conditions were found to be contaminated with aflatoxins B(1) and B(2) as were the fractions. The sums of AFB(1) and AFB(2) in stored paddy rice, hulls, brown rice, bran and white rice were 141, 39, 158, 367 and 56?μg?kg(-1), respectively. The ratio of aflatoxin B(1) and B(2) was about 10?:?1. AFG(1) and AFG(2) were less than 1?μg?kg(-1). Thus, brown rice contained 92.9% of the aflatoxins in paddy rice, whereas white rice contained only 27.9%.     

Antimony (Sb) and arsenic (As) in Sb mining impacted paddy soil from Xikuangshan, China: differences in mechanisms controlling soil sequestration and uptake in rice

Foods produced on soils impacted by antimony (Sb) mining activities are a potential health risk due to plant uptake of the contaminant metalloids (Sb) and arsenic (As). Here we report for the first time the chemical speciation of Sb in soil and porewater of flooded paddy soil, impacted by active Sb mining, and its effect on uptake and speciation in rice plants (Oryza sativa L. cv Jiahua). Results are compared with behavior and uptake of As. Pot experiments were conducted under controlled conditions in a climate chamber over a period of 50 days. In pots without rice plants, flooding increased both the concentration of dissolved Sb (up to ca. 2000 μg L(-1)) and As (up to ca. 1500 μg L(-1)). When rice was present, Fe plaque developing on rice roots acted as a scavenger for both As and Sb, whereby the concentration of As, but not Sb, in porewater decreased substantially. Dissolved Sb in porewater, which occurred mainly as Sb(V), correlated with Ca, indicating a solubility governed by Ca antimonate. No significant differences in bioaccumulation factor and translocation factor between Sb and As were observed. Greater relative concentration of Sb(V) was found in rice shoots compared to rice root and porewater, indicating either a preferred uptake of Sb(V) or possibly an oxidation of Sb(III) to Sb(V) in shoots. Adding soil amendments (olivine, hematite) to the paddy soil had no effect on Sb and As concentrations in porewater.     

Arsenic Bioaccessibility in Cooked Rice as Affected by Arsenic in Cooking Water

Abstract: Rice can easily accumulate arsenic (As) into its grain and is known to be the highest As‐containing cereal. In addition, the As burden in rice may increase during its processing (such as when cooking using As‐polluted water). The health risk posed by the presence of As in cooked rice depends on its release from the matrix along the digestive system (bioaccessibility). Two types of white polished long‐grain rice, namely, nonparboiled and parboiled (total As: 202 and 190 μg As kg^?1, respectively), were cooked in excess of water with different levels of As (0, 10, 47, 222, and 450 μg As L^?1). The bioaccessibility of As from these cooked rice batches was evaluated with an in vitro dynamic digestion process. Rice cooked with water containing 0 and 10 μg As L^?1 showed lower As concentrations than the raw (uncooked) rice. However, cooking water with relatively high As content (≥47 μg As L^?1) significantly increased the As concentration in the cooked rice up to 8‐ and 9‐fold for the nonparboiled and parboiled rice, respectively. Parboiled rice, which is most widely consumed in South Asia, showed a higher percentage of As bioaccessibility (59% to 99%) than nonparboiled rice (36% to 69%) and most of the As bioaccessible in the cooked rice (80% to 99%) was released easily during the first 2 h of digestion. The estimation of the As intake through cooked rice based on the As bioaccessibility highlights that a few grams of cooked rice (less than 25 g dry weight per day) cooked with highly As contaminated water is equivalent to the amount of As from 2 L water containing the maximum permissible limit (10 μg As L^?1). Practical Application: Studies on As bioaccessibility are needed for determining human As intake from rice for use in accurate risk assessments to establish updated legislation regarding maximum level of As in food. High As bioaccessibility from parboiled rice (consumed by the majority of the people in South Asia), and the findings of high As levels in discarded rice gruel (fed to livestock), has implications for human and animal health.     

Effect of two different rice dehusking procedures on total arsenic concentration in rice

Pollution of subterranean water by arsenic (As) in Asia has resulted in the worst chemical disaster in human history. For populations living on subsistence rice diets, As contamination of rice grain contributes greatly to dietary As exposure. The main objectives of this study were to compare two dehusking processes: (a) wet process (soaking of rice, boiling and mechanical hulling) and (b) dry process (mechanical hulling), and recommend the method leading to a lower As content in commercial rice. In general, hulling of paddy rice (373 μg As kg⁻¹) significantly decreased As content in rice grain (311 μg As kg⁻¹). The final As concentrations in boiled rice (final product of the wet process) and atab rice (dry process) were 332 and 290 μg kg⁻¹. Thus, the dry method is recommended for dehusking paddy rice if not As-free water is available. However, villagers can reduce the As content in the wet system by discarding the soaking water and using new water for the light boiling. Finally, it is not recommended to use rice husk for feeding animals because the As concentration is very high, approximately 1,000 μg As kg⁻¹.     

Arsenic in rice: I. Estimating normal levels of total arsenic in rice grain

High levels of arsenic (As) in rice grain are a potential concern for human health. Variability in total As in rice was evaluated using 204 commercial rice samples purchased mostly in retail stores in upstate New York and supplemented with samples from Canada, France, Venezuela, and other countries. Total As concentration in rice varied from 0.005 to 0.710 mg kg(-1). We combined our data set with literature values to derive a global "normal" range of 0.08-0.20 mg kg(-1) for As concentration in rice. The mean As concentrations for rice from the U.S. and Europe (both 0.198 mg kg(-1)) were statistically similar and significantly higher than rice from Asia (0.07 mg kg(-1)). Using two large data sets from Bangladesh, we showed that As contaminated irrigation water, but not soil, led to increased grain As concentration. Wide variability found in U.S. rice grain was primarily influenced by region of growth rather than commercial type, with rice grown in Texas and Arkansas having significantly higher mean As concentrations than that from California (0.258 and 0.190 versus 0.133 mg kg(-1)). Rice from one Texas distributor was especially high, with 75% of the samples above the global "normal" range, suggesting production in an As contaminated environment.