Heavy metals in foods – Part 5

Arsenic measurement methods

Soluble inorganic arsenic is acutely toxic, and ingestion of large doses leads to gastrointestinal symptoms, disturbances of cardiovascular and nervous system functions, and eventually death. In survivors, bone marrow depression, hemolysis, hepatomegaly, Melanesia, polyneuropathy and encephalopathy may be observed.

Chronic arsenic exposure in Taiwan has been shown to cause black foot disease (BFD), a severe form of peripheral vascular disease (PVD) which leads to gangrenous changes. This disease has not been documented in other parts of the world, and the findings in Taiwan may depend upon other contributing factors. However, there is good evidence from studies in several countries that arsenic exposure causes other forms of PVD.

Conclusions on the causality of the relationship between arsenic exposure and other health effects are less clear-cut. The evidence is strongest for hypertension and cardiovascular disease, suggestive for diabetes and reproductive effects and weak for cerebrovascular disease, long-term neurological effects, and cancer at sites other than lung, bladder, kidney and skin

The determination of inorganic arsenic (iAs) in food is considered to be a subject of paramount importance. Of the great number of known arsenic species that have been identified in different types of food, arsenic health concerns are derived primarily from the inorganic forms of this element. Moreover, food is the main contributor to human arsenic intake (excluding occupational exposure and drinking contaminated water. This interest is supported by a huge number of publications in the literature over many years. The causal effect of arsenic with regards to cancer was well studied more than twenty years ago.

The toxic effects of inorganic arsenic forms led the Joint Commission Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO) in 1989 to set a provisional tolerable weekly intake (PTWI) for inorganic arsenic of 15 µg/kg of body weight (equivalent to 2.1 µg/kg bodyweight per day). Recently, the European Food Safety Authority (EFSA) and the Joint FAO/WHO Expert Committee on Food Additives (JECFA) evaluated dietary exposure to iAs. Both concluded that the PTWI parameter is no longer appropriate and should no longer be used, and it is thus withdrawn. The EFSA and JECFA evaluations provided estimates of toxic intake limits for iAs as a benchmark dose level (BMDL): 0.3–8 µg/kg body weight per day for cancers of lung, skin, and bladder as well as for skin lesions (EFSA BMDL01); and 3.0 µg/kg body weight per day (2–7 µg kg−1 body weight per day based on the estimated range of total dietary exposure) for lung cancer (JECFA BMDL0,5). In addition, both reports emphasized the need to produce speciation data, particularly iAs data, for different food products to estimate the health risk associated with dietary As exposure. The European Food Safety Authority and JECFA highlighted the need for a robust, validated analytical method for the determination of iAs in a range of food items; and the need for certified reference materials (CRMs) for iAs. In 2014, EFSA evaluated dietary exposure to iAs in the European population. It concluded that for all ages except infants and toddlers, the main contributor to dietary exposure to iAs is the food group “grain-based processed products (non-rice-based)”. Other food groups that were important contributors to iAs exposure were rice, milk, and dairy products (the main contributor in infants and toddlers), and drinking water. Furthermore, in order to reduce the uncertainty in the assessment of exposure to iAs, more analytical data on iAs are needed. This mainly refers to speciation data in fish and seafood, and for food groups that contribute substantially to dietary exposure to iAs (e.g., rice and wheat-based products). Rice and rice-based products are the type of food in which iAs toxicity is of most concern in many countries, especially in countries, such as those in Southeast Asia, where irrigation practices increasingly include flooding with water that contains arsenic. This can lead to an increase of the arsenic content of rice, and so control of such practices is frequently called for. The other types of food product that merits special interest regarding iAs toxicity are those with a marine origin and to a lesser extent other food commodities such as apple juice and mushrooms. Furthermore, the assessment of iAs concentrations in food products that are particularly aimed at children deserves special interest. Other studies also reveal that knowledge of iAs content is important in the control of processes of biotransformation in the marine organisms that constitute a food source after exposure to iAs compounds. It was considered four food groups, in accordance with their iAs content, reporting estimated mean values as: seaweed/algae/seafood, 11 000  µg/kg for seaweed/algae and 130  µg/kg for seafood; rice, 130  µg/kg; apple juice, 5.8  µg/kg; and infant food, rice, other cereals, and related products, 92  µg/kg; and vegetables, 20  µg/kg.

 

The establishment of maximum levels (MLs) regulating iAs are emphasized in Directives and Regulations. Meharg and Raab discuss several proposals and relates them to detection capacities and the availability of measurement techniques, highlighting the assessment of iAs content. Among the regulations proposing MLs of arsenic tolerated in food, few establish specific levels for iAs. The maximum tolerable level of total arsenic (tAs) in drinking water defined by the World Health Organization (WHO) is 10  µg/L. Recently, the European Union published Regulation (EU) 2015/100658 amending Annex to Regulation (EC) No 1881/200661 regarding the maximum levels of iAs in foodstuffs, especially rice and rice-based products. The new MLs of iAs range from 0.10 mg to 0.3 mg As per Kg depending of the rice product. Furthermore, the EU established a maximum level for iAs in animal feeds: a content of below 2 mg/kg is recommended, especially for those based on the seaweed species Hizikia fusiforme. The Ministry of Health of China established a maximum level of iAs in food products depending on the type of food. The CODEX Alimentarius Commission in a draft report on contaminants in food accepts a ML of 0.2 mg/kg of iAs for polished rice and analysis of tAs as a screening method; the same document states that no agreement was reached for a ML of iAs in husked rice, but a value of 0.4 mg/kg is subject to ongoing discussion and may be adopted at the next session of the Committee. The Australia New Zealand Food Standard Code (FSANZ) established a limit of 1 mg/kg for seaweed and mollusks; while for crustacean and fish, iAs is not allowed to exceed 2 mg/kg. Meanwhile, the authorities in the UK have advised consumers to avoid consumption of hijiki seaweed, while the Canadian Food Inspection Agency (CFIA) advises consumers to avoid that seaweed. Specific regulations for iAs in edible seaweed have been established in some countries: 3 mg/kg dry weight (dw) as the maximum permitted level in the USA and France. The content of iAs in apple juices is considered to be a matter of concern by the US Food Drug and Administration (FDA) and by the FSANZ. The FDA recommends 10 parts per billion (ppb), as in drinking water, as a ML for iAs adequate to protect public health. The Canadian government, through Health Canada, established 0.1 parts per million (ppm) as the maximum tolerated limit for arsenic in fruit juices, fruit nectar, and ready-to-serve beverages; furthermore, this organization is currently considering establishing a specific lower tolerance of 0.01 ppm for apple juice. Several national initiatives and authorities have advised against consumption of rice drinks for infants and toddlers because it can increase the intake of iAs. The UK Food Standards Agency does not recommend substitution of breast milk, infant formula, or cows’ milk by rice drinks for toddlers and young children up to 4.5 years, whereas the Swedish National Food Agency recommends no rice-based drinks for children younger than six years and, in Denmark, children are advised against consuming rice drinks and biscuits.

The analytical technology to be applied for the assessment of arsenic species, highlighting iAs, is continuously updated and reviewed. Nearing et al. reviewed additional analytical methods suitable for obtaining data to complement the information on arsenic speciation obtained when applying the methods commonly used. Among such complementary methods, electrospray mass spectrometry (ESI-MS) is most useful for identifying or complementing information on several arsenic compounds with more complex molecular structures than those corresponding to iAs species. Some articles report the use of some supplementary methods for iAs. Among them Nearing et al. report X-ray absorption near edge structure (XANES) for As speciation in solid samples to obtain information on which As species cannot be extracted, provided that enough mass remain after extraction, as complementary information for high performance liquid chromatography with inductively coupled plasma mass spectrometry (HPLC-ICP-MS), and Whaley-Martin, in a study on arsenic species distribution in marine periwinkle tissues samples using HPLC-ICP-MS, uses X-ray spectroscopy (XAS) for the estimation of inorganic arsenic species and to reveal high concentrations in contaminated samples. Some other general reviews of element speciation provide broad information on arsenic speciation, including analytical methodology and types of food. Moreover, the importance of maintaining the integrity of arsenic species during the overall analytical process, with final measurement using HPLC-ICP-MS and hydride generation–atomic fluorescence spectrometry (HG-AFS), should be considered

Efforts have also been made in the last decades by research scientists, government agencies (FDA and EPA), and commercial laboratories to establish methodologies for the specific determination of iAs in food products. The validation of such methods is mandatory to demonstrate their suitability for routine analysis in control laboratories. Reliable analytical methods are currently available, and it can be expected that they will be considered in future regulations from government agencies. The European Committee for Standardization (CEN) (CEN TC 327/WG 4) standardized a method (EN 16278:2012) for the determination of iAs in animal feeding stuffs by hydride generation–atomic absorption spectrometry (HG-AAS) after microwave extraction and off-line separation of iAs by solid-phase extraction (SPE). Other two standards are published, such as Chinese Standard Method GB/T 5009.11-200395 and EN 15517:2008.96 Currently, there is an ongoing proposal for a CEN method to determine iAs in foodstuffs by HPLC coupled to ICP-MS (CEN TC275/WG10). The Association of Official Agricultural Chemists (AOAC), through AOAC International, invited method authors and developers to submit methods for quantitation of arsenic species in selected foods and beverages that propose to meet the AOAC Standard Method Performance Requirements (SMPR), 2015.006 for quantitation of arsenic species in selected foods and beverages; and the preferred analytical technique for quantitation is HPLC-ICP-MS. This proposal is currently in its fourth draft version. Furthermore, for future implementation of analytical methods for iAs determination in food control laboratories, the availability of validated methods as well as participation in proficiency testing (PT) and the analysis of CRMs is mandatory, according to the ISO/IEC 17025 standard. Obviously, this is applicable to speciation of iAs in food, considering its toxicity and the need to develop methods that can be applied in routine analysis.