Does the determination of inorganic arsenic in rice depend on the method?

Recent developments in speciation and determination of arsenic in marine organisms using different analytical techniques. A review

Marine organisms play a vital role as the main providers of essential and functional food. Yet they also constitute the primary pathway through which humans are exposed to total arsenic (As) in their diets. Since it is well known that the toxicity of this metalloid ultimately depends on its chemical forms, speciation in As is an important issue. Most relevant articles about arsenic speciation have been investigated. This extended not only from general knowledge about As but also the toxicity and health related issues resulting from exposure to these As species from the food ecosystem. There can be enormous side effects originating from exposure to As species that must be measured quantitatively. Therefore, various convenient approaches have been developed to identify different species of As in marine samples. Different extraction strategies have been utilized based on the As species of interest including water, methanol and mixtures of both, and many other extraction agents have been explained in this article. Furthermore, details of hyphenated techniques which are available for detecting these As species have been documented, especially the most versatile and applied technique including inductively coupled plasma mass spectrometry.

Arsenic and cadmium contents in Brazilian rice from different origins can vary more than two orders of magnitude

Brazil is a major producer of rice, but there is not enough information about As and Cd in rice grown under different conditions in this country. Here, As and Cd were determined by ICP-MS and species of As by HPLC-ICP-MS in Brazilian husked rice, covering diverse cultivars and regions, as well as upland and flooded production systems. Significant differences were observed for contents of both elements according to the origin of rice. All samples were below the maximum limit for Cd (400 µg/kg) set by national legislation, while nine samples presented total As above the legislation limit (300 µg/kg). From 24 samples analyzed for As species, 42% showed iAs above the European limit for production of food to infants (100 µg/kg). The total As content in samples from Mato Grosso state presented a maximum value of 6 µg/kg, which combined with low Cd content make interesting further studies.

Inter-laboratory validation of an inexpensive streamlined method to measure inorganic arsenic in rice grain

With the establishment by CODEX of a 200 ng/g limit of inorganic arsenic (iAs) in polished rice grain, more analyses of iAs will be necessary to ensure compliance in regulatory and trade applications, to assess quality control in commercial rice production, and to conduct research involving iAs in rice crops. Although analytical methods using high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) have been demonstrated for full speciation of As, this expensive and time-consuming approach is excessive when regulations are based only on iAs. We report a streamlined sample preparation and analysis of iAs in powdered rice based on heated extraction with 0.28 M HNO₃ followed by hydride generation (HG) under control of acidity and other simple conditions. Analysis of iAs is then conducted using flow-injection HG and inexpensive ICP-atomic emission spectroscopy (AES) or other detection means. A key innovation compared with previous methods was to increase the acidity of the reagent solution with 4 M HCl (prior to reduction of As⁵⁺ to As³⁺), which minimized interferences from dimethylarsinic acid. An inter-laboratory method validation was conducted among 12 laboratories worldwide in the analysis of six shared blind duplicates and a NIST Standard Reference Material involving different types of rice and iAs levels. Also, four laboratories used the standard HPLC-ICP-MS method to analyze the samples. The results between the methods were not significantly different, and the Horwitz ratio averaged 0.52 for the new method, which meets official method validation criteria. Thus, the simpler, more versatile, and less expensive method may be used by laboratories for several purposes to accurately determine iAs in rice grain. Graphical abstract Comparison of iAs results from new and FDA methods.

Human exposure to organic arsenic species from seafood

Seafood, including finfish, shellfish, and seaweed, is the largest contributor to arsenic (As) exposure in many human populations. In contrast to the predominance of inorganic As in water and many terrestrial foods, As in marine-derived foods is present primarily in the form of organic compounds. To date, human exposure and toxicological assessments have focused on inorganic As, while organic As has generally been considered to be non-toxic. However, the high concentrations of organic As in seafood, as well as the often complex As speciation, can lead to complications in assessing As exposure from diet. In this report, we evaluate the presence and distribution of organic As species in seafood, and combined with consumption data, address the current capabilities and needs for determining human exposure to these compounds. The analytical approaches and shortcomings for assessing these compounds are reviewed, with a focus on the best practices for characterization and quantitation. Metabolic pathways and toxicology of two important classes of organic arsenicals, arsenolipids and arsenosugars, are examined, as well as individual variability in absorption of these compounds. Although determining health outcomes or assessing a need for regulatory policies for organic As exposure is premature, the extensive consumption of seafood globally, along with the preliminary toxicological profiles of these compounds and their confounding effect on assessing exposure to inorganic As, suggests further investigations and process-level studies on organic As are needed to fill the current gaps in knowledge.

Human exposure to dietary inorganic arsenic and other arsenic species: State of knowledge, gaps and uncertainties

Inorganic arsenic (iAs) is ubiquitous in the environment as arsenite (AsIII) and arsenate (AsV) compounds and biotransformation of these toxic chemicals leads to the extraordinary variety of organoarsenic species found in nature. Despite classification as a human carcinogen based on data from populations exposed through contaminated drinking water, only recently has a need for regulatory limits on iAs in food been recognized. The delay was due to the difficulty in risk assessment of dietary iAs, which critically relies on speciation analysis providing occurrence data for iAs in food - and not simply for total arsenic. In the present review the state of knowledge regarding arsenic speciation in food and diet is evaluated with focus on iAs and human exposure assessment through different dietary approaches including duplicate diet studies, market basket surveys, and total diet studies. The analytical requirements for obtaining reliable data for iAs in food are discussed and iAs levels in foods and beverages are summarized, along with information on other (potentially) toxic co-occurring organoarsenic compounds. Quantitative exposure assessment of iAs in food is addressed, focusing on the need of capturing variability and extent of exposure and identifying what dietary items drive very high exposure for certain population groups. Finally, gaps and uncertainties are discussed, including effect of processing and cooking, and iAs bioavailability.

State of the art in the determination of trace elements in seawater: a worldwide proficiency test

This manuscript presents the results of the International Measurement Evaluation Programme 40 (IMEP-40) study, a proficiency test (PT) which was organised to assess the worldwide performance of laboratories for the determination of trace elements in seawater. This PT supports the implementation of the European Union Water Framework Directive 2000/60/EC, which aims at achieving a long-term high level protection of the aquatic environment, covering lakes, ground water and coastal waters. Forty-six participants reported results. The test item was seawater containing the trace elements As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se and Zn. The trace elements in the test item were present in very low concentrations to mimic natural levels. The results of the participants were rated with z and zeta (ζ) scores in accordance with ISO 13528 and ISO 17043. The standard deviation for proficiency assessment, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \widehat{\upsigma} $$\end{document}σ^, was set at 25 % of the respective assigned values for the 12 measured elements based on previous experience with similar PTs. The low levels of the trace elements combined with the high salt concentration of the seawater made the measurements challenging. Many laboratories were unable to detect or quantify the elements and reported “lower than X” values. The percentage of satisfactory performances (expressed as z scores) ranged from 41 % (Cr, Fe) to 86 % (Mo). The PT study showed that the use of proper standard methods, like ISO 17294-2, and sensitive techniques, like inductively coupled plasma mass spectrometry (ICP-MS), contributed to performing well in this PT round.

Recent Advances in the Measurement of Arsenic, Cadmium, and Mercury in Rice and Other Foods

Trace element analysis of foods is of increasing importance because of raised consumer awareness and the need to evaluate and establish regulatory guidelines for toxic trace metals and metalloids. This paper reviews recent advances in the analysis of trace elements in food, including challenges, state-of-the-art methods, and use of spatially resolved techniques for localizing the distribution of arsenic and mercury within rice grains. Total elemental analysis of foods is relatively well-established, but the push for ever lower detection limits requires that methods be robust from potential matrix interferences, which can be particularly severe for food. Inductively coupled plasma mass spectrometry (ICP-MS) is the method of choice, allowing for multi-element and highly sensitive analyses. For arsenic, speciation analysis is necessary because the inorganic forms are more likely to be subject to regulatory limits. Chromatographic techniques coupled to ICP-MS are most often used for arsenic speciation, and a range of methods now exist for a variety of different arsenic species in different food matrices. Speciation and spatial analysis of foods, especially rice, can also be achieved with synchrotron techniques. Sensitive analytical techniques and methodological advances provide robust methods for the assessment of several metals in animal- and plant-based foods, particularly for arsenic, cadmium, and mercury in rice and arsenic speciation in foodstuffs.

Fast ion chromatography-ICP-QQQ for arsenic speciation

Two methods for the fast separation of arsenic species are presented. The general approach is to modify existing methodology utilizing carbonate eluents for a small particle size, short column length Hamilton PRPX100 column which is interfaced with the Agilent 8800 ICP-QQQ using oxygen as reaction gas and detection of AsO at m/z 91. Using H₂O₂ in the extractant to oxidize As(III) to As(V) it is possible to separate arsenobetaine from DMA, MMA and As(V) in 1.5 minutes. Such a method may be useful where a measure of total inorganic As is sufficient, for example for regulatory compliance in food or beverage testing. It is possible to separate six As species. i.e the four above and arsenocholine and As(III) in 4.5 minutes using a gradient separation. Such a method could be useful analysis of urinary arsenic species. Coupling with high sensitivity of ICP-QQQ yields equivalent or better detection limits than conventional methods with run times up to 5 times faster, which is a significant benefit for sample throughput and method development.

Enzyme-assisted extraction and liquid chromatography mass spectrometry for the determination of arsenic species in chicken meat

Chicken is the most consumed meat in North America. Concentrations of arsenic in chicken range from μg kg(-1) to mg kg(-1). However, little is known about the speciation of arsenic in chicken meat. The objective of this research was to develop a method enabling determination of arsenic species in chicken breast muscle. We report here enzyme-enhanced extraction of arsenic species from chicken meat, separation using anion exchange chromatography (HPLC), and simultaneous detection with both inductively coupled plasma mass spectrometry (ICPMS) and electrospray ionization tandem mass spectrometry (ESIMS). We compared the extraction of arsenic species using several proteolytic enzymes: bromelain, papain, pepsin, proteinase K, and trypsin. With the use of papain-assisted extraction, 10 arsenic species were extracted and detected, as compared to 8 detectable arsenic species in the water/methanol extract. The overall extraction efficiency was also improved using a combination of ultrasonication and papain digestion, as compared to the conventional water/methanol extraction. Detection limits were in the range of 1.0-1.8 μg arsenic per kg chicken breast meat (dry weight) for seven arsenic species: arsenobetaine (AsB), inorganic arsenite (As(III)), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), inorganic arsenate (As(V)), 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone), and N-acetyl-4-hydroxy-m-arsanilic acid (NAHAA). Analysis of breast meat samples from six chickens receiving feed containing Roxarsone showed the presence of (mean±standard deviation μg kg(-1)) AsB (107±4), As(III) (113±7), As(V) (7±2), MMA (51±5), DMA (64±6), Roxarsone (18±1), and four unidentified arsenic species (approximate concentration 1-10 μg kg(-1)).

Speciation without chromatography using selective hydride generation: inorganic arsenic in rice and samples of marine origin

Because of the toxicity of inorganic arsenic (iAs), only iAs needs to be monitored in food and feedstuff. This demands the development of easy and quick analytical methods to screen large number of samples. This work focuses on hydride generation (HG) coupled with an ICPMS as an arsenic detector where the HG is added as a selective step to determine iAs in the gaseous phase while organically bound As remains in the solution. iAs forms volatile arsine species with high efficiency when treated with NaBH4 at acidic conditions, whereas most other organoarsenic compounds do not form any or only less volatile arsines. Additionally, using high concentrations of HCl further reduces the production of the less volatile arsines and iAs is almost exclusively formed, therefore enabling to measure iAs without a prior step of species separation using chromatography. Here, we coupled a commercially available HG system to an ICPMS and optimized for determination of iAs in rice and samples of marine origin using different acid concentrations, wet and dry plasma conditions, and different reaction gas modes. Comparing this method to conventional HPLC-ICPMS, no statistical difference in iAs concentration was found and comparable limits of detections were achieved using less than half the instrument time.

Transformation of arsenic species during in vitro gastrointestinal digestion of vegetables

Arsenic is an element widely distributed in the environment, and the diet is the main source of arsenic exposure for most people. However, many of the processes related to steps before intestinal absorption are unknown. This study evaluates the effect of in vitro gastrointestinal digestion on pentavalent arsenic forms [As(V), MMA(V), DMA(V)] present in various vegetables (garlic, broccoli, asparagus, spinach) after soaking or boiling in aqueous solutions of these species. The results showed that the gastrointestinal digest contained trivalent or thiolated arsenic forms different from the pentavalent species added initially. Transformation percentages varied, depending on sample, treatment, and arsenic species. Results showed transformation of up to 22% to As(III), 35% to MMA(III)/MMAS, and 26% to DMA(III)/DMAS. These data indicate that more toxic arsenic species are present in the gastrointestinal digest, and they highlight the need to consider this process when evaluating the toxicological risk associated with ingestion of this metalloid.

Inorganic arsenic in seafood: does the extraction method matter?

Nine different extraction methods were evaluated for three seafood samples to test whether the concentration of inorganic arsenic (iAs) determined in seafood is dependent on the extraction method. Certified reference materials (CRM) DOLT-4 (Dogfish Liver) and TORT-2 (Lobster Hepatopancreas), and a commercial herring fish meal were evaluated. All experimental work described here was carried out by the same operator using the same instrumentation, thus eliminating possible differences in results caused by laboratory related factors. Low concentrations of iAs were found in CRM DOLT-4 (0.012±0.003mgkg(-1)) and the herring fish meal sample (0.007±0.002mgkg(-1)) for all extraction methods. When comparing the concentration of iAs in CRM TORT-2 found in this study and in the literature dilute acids, HNO3 and HCl, showed the highest extracted iAs wheras dilute NaOH (in 50% ethanol) showed significantly lower extracted iAs. However, most other extraction solvents were not statistically different from one another.

Measurement of inorganic arsenic species in rice after nitric acid extraction by HPLC-ICPMS: verification using XANES

The measurement of As species in rice is normally accomplished by extraction followed by HPLC-ICPMS analysis. This method, however, has not been comprehensively validated by comparing these speciation results with XANES, which does not require sample extraction, due to the challenge of conducting XANES analysis at very low As concentrations. In this study As speciation data using nitric acid extraction/HPLC-ICPMS and XANES are compared to verify the efficacy of using 2% v/v nitric acid extraction and HPLC-ICPMS to measure inorganic As, DMA, and MA in reference rice materials and common rice varieties obtainable in Australia. Total As and As species (As(III), As(V), DMA, and MA) concentrations measured in 8 reference materials were in agreement with published values. XANES analysis was performed on 5 samples having total As concentrations ranging from 0.198 to 0.335 μg g(-1). XANES results gave similar proportions of total As(III), As(V), and DMA to HPLC-ICPMS. XANES was able to distinguish two forms of As(III): As(III) and As(III)GSH. Total As concentrations in rice samples varied from 0.006 to 0.45 μg g(-1) As (n = 47) with a mean ± std of 0.127 ± 0.112 μg g(-1) As with most As present as inorganic species (63 ± 26%). DMA was found in nearly all the rice samples with the majority of samples containing concentrations below 0.05 μg g(-1) As while MA concentrations were negligible (<0.003 μg g(-1) As). Six rice varieties produced in Australia, China, and Spain all had elevated DMA concentrations (0.170-0.399 μg g(-1) As) that were correlated with total As concentrations (r(2) = 0.7518). In conclusion, comparison of As speciation by HPLC-ICPMS and XANES showed that similar As species were detected indicating the appropriateness of using 2% v/v nitric acid for extraction of rice prior to speciation. Common rice varieties obtainable in Australia generally have low As concentrations with most As present as inorganic As.

The Determination of Arsenic Compounds: A Critical Review

A large number of publications describe the determination of arsenic in “environmental” samples in the broadest sense, a substantial subset of which focus on plant-based foodstuffs. There is a considerable interest in the inorganic arsenic content of food, especially rice, as there is recent evidence that concentrations may be high enough to exceed acceptable risk thresholds. The methodology for the determination of arsenic in rice is critically evaluated and results (a) for a rice flour reference material (National Institute of Standards SRM 1568a, certified only for total arsenic) and (b) a recent proficiency test (run by the European Commission's Joint Research Centre Institute for Reference Materials and Measurement) are examined. Difficulties with this particular analysis may lie in the sample preparation stages, over which there is still disagreement with regard to species stability, though a simple, hot-water extraction may be sufficient. High performance liquid chromatography separations with plasma-source mass spectrometry detection are popular; however, chromatographic separations are often not adequately described, the enhancement effect of carbon-containing species is often overlooked, and the fate of chlorine-containing species, responsible for an isobaric overlap interference, often obscure. Compound-dependent responses, for which there is a plenty of evidence, are almost never acknowledged or discussed.

Is it possible to agree on a value for inorganic arsenic in food? The outcome of IMEP-112

Two of the core tasks of the European Union Reference Laboratory for Heavy Metals in Feed and Food (EU-RL-HM) are to provide advice to the Directorate General for Health and Consumers (DG SANCO) on scientific matters and to organise proficiency tests among appointed National Reference Laboratories. This article presents the results of the 12th proficiency test organised by the EU-RL-HM (IMEP-112) that focused on the determination of total and inorganic arsenic in wheat, vegetable food and algae. The test items used in this exercise were: wheat sampled in a field with a high concentration of arsenic in the soil, spinach (SRM 1570a from NIST) and an algae candidate reference material. Participation in this exercise was open to laboratories from all around the world to be able to judge the state of the art of the determination of total and, more in particular, inorganic arsenic in several food commodities. Seventy-four laboratories from 31 countries registered to the exercise; 30 of them were European National Reference Laboratories. The assigned values for IMEP-112 were provided by a group of seven laboratories expert in the field of arsenic speciation analysis in food. Laboratory results were rated with z and ζ scores (zeta scores) in accordance with ISO 13528. Around 85 % of the participants performed satisfactorily for inorganic arsenic in vegetable food and 60 % did for inorganic arsenic in wheat, but only 20 % of the laboratories taking part in the exercise were able to report satisfactory results in the algae test material.

Speciation and monitoring test for inorganic arsenic in white rice flour

A monitoring test for arsenic species in white rice flour was developed and applied to flours made from 20 samples of polished rice collected from locations all over Japan. The arsenic species in white rice flour made from five samples each of four types of rice were analyzed by HPLC-ICP-MS after a heat-assisted aqueous extraction. The total arsenic and major and minor element concentrations in the white rice flours were measured by ICP-MS and ICP-OES after microwave-assisted digestion. 91 ± 1% of the arsenic in the flours was extractable. Concentrations of arsenite [As(III)], arsenate [As(V)], and dimethylarsinic acid (DMAA) were closely positively correlated with the total arsenic concentrations. The total arsenic concentration in flours made from rice collected around Japan was 0.15 ± 0.07 mg kg(-1) (highest, 0.32 mg kg(-1)), which is very low. It was thus confirmed that the white rice flour samples collected in this experiment were not suffered from noticeable As contamination.

A fully validated method for the determination of arsenic species in rice and infant cereal products

A full validation of inorganic arsenic (iAs), methylarsonic acid (MA), and dimethyl arsinic acid (DMA) in several types of rice and rice-based infant cereals is reported. The analytical method was developed and validated in two laboratories. The extraction of the As species was performed using nitric acid 0.2 % and hydrogen peroxide 1 %, and the coupled system liquid chromatography-inductively coupled plasma-mass spectrometry (LCICP-MS) was used for speciation measurements. Detection limit (DL), quantification limit, linearity, precision, trueness, accuracy, selectivity, as well as expanded uncertainty for iAs, MA, and DMA were established. The certified reference materials (CRMs) (NMIJ 7503a, NCS ZC73008, NIST SRM 1568a) were used to check the accuracy. The method was shown to be satisfactory in two proficiency tests (PTs). The broad applicability of the method is shown from the results of analysis of 29 samples including several types of rice, rice products, and infant cereal products. Total As ranged from 40.1 to 323.7 μg As kg–1. From the speciation results, iAs was predominant, and DMA was detected in some samples while MA was not detected in any sample.

Determination of inorganic arsenic in seafood: Emphasizing the need for certified reference materials

To evaluate the accuracy and robustness of an extraction method, utilizing an -alkaline-ethanolic solution and microwave heating, the certified reference material (CRM) TORT-2 was subjected to three different instrumental methodologies: high-performance liquid chromatography (HPLC), coupled with and without post-column hydride generation; inductively coupled plasma-mass spectrometry (ICP-MS); and HPLC-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS). The three methods gave a consistent value of inorganic arsenic (As) which is near the mean value of the reported values in the literature, which, however, range by a factor of 10. Inorganic As, defined here as all As species that do not have an As–C bond, that is, the sum of arsenite and arsenate and any thiol-bound As, was found to be less than 4 % of total As concentration in 12 samples of fish meal when subjected to this extraction method followed by HPLC-ICP-MS. To date, there is no certified value of inorganic As in a seafood-based reference material to compare to in order to validate the findings. This illustrates the difficulties in quantitative determination of inorganic As in seafood and the need for a reference material for inorganic As and proficiency tests in order to introduce legislation for a maximum level of inorganic As in seafood and feed.

Determination of water-soluble arsenic compounds in commercial edible seaweed by LC-ICPMS

This paper reports arsenic speciation in edible seaweed (from the Galician coast, northwestern Spain) produced for human consumption. Chondrus crispus , Porphyra purpurea , Ulva rigida , Laminaria ochroleuca , Laminaria saccharina , and Undaria pinnatifida were analyzed. The study focused on arsenosugars, the most frequently occurring arsenic species in algae. As(III) and As(V) were also determined in aqueous extracts. Total arsenic in the samples was determined by microwave digestion and inductively coupled plasma mass spectrometry (ICPMS). For arsenic speciation, a water extraction especially suitable for arsenosugars was used, and the arsenic species were analyzed by liquid chromatography with both anionic and cationic exchange and ICPMS detection (LC-ICPMS). The total arsenic content of the alga samples ranged from 5.8 to 56.8 mg As kg(-1). The mass budgets obtained in the extracts (column recovery × extraction efficiency) ranged from 38 to 92% except for U. pinnatifida (4%). The following compounds were detected in the extracts: arsenite (As(III)), arsenate (As(V)), methylarsonate (MA), dimethylarsinate (DMA), sulfonate sugar (SO(3)-sug), phosphate sugar (PO(4)-sug), arsenobetaine (AB), and glycerol sugar (Gly-sug). The highest concentrations corresponded to the arsenosugars.