Dietary exposure to total and inorganic arsenic via rice and rice-based products consumption
Graphical abstract
Introduction
Arsenic (As) is a metalloid that generally acts as a metal (Nigra et al., 2017). It is widely distributed in the Earth's crust and can react with oxygen, chlorine and sulphur to form inorganic compounds, and with carbon and hydrogen to form organic compounds (Jomova et al., 2011). Arsenic is on the top 1 on the substance priority list of the Agency for Toxic Substances and Disease Registry (ATSDR, 2017).
The natural release of inorganic arsenic (InAs) to the environment is caused by the alteration and erosion of rocks and soil, where it is present as arsine, arsenite, arsenate, and oxide. In turn, anthropogenic sources include mining, metallurgical activity, use of pesticides, and combustion of different materials, such as coal and wood. The incineration of domestic and urban waste is also an important source (Margallo et al., 2015; Rovira et al., 2015, 2018).
The major route of exposure to arsenic is diet, while other pathways, like dermal and inhalation are less important (Chung et al., 2014). Organic arsenic is mainly found in products of marine origin, such as fish and seafood. This food group contains foodstuffs with the highest concentrations of the organic form of arsenic: dimethylarsenic (DMA) (Taylor et al., 2017). In fact, fish, crustaceans, molluscs and other aquatic animals have the ability to metabolize arsenic and accumulate it as DMA. DMA has a notable lower toxicity than the inorganic forms, being primarily excreted through the urine (Hughes, 2002).
On the other hand, InAs is found in water in certain geographical areas, and in rice and rice products (Hojsak et al., 2015). In addition, it should be highlighted that the inorganic forms of arsenic are the most toxic. The International Agency for Research on Cancer (IARC) catalogues arsenic as a known carcinogen, category 1 (carcinogenic to humans, with sufficient epidemiological evidence), while the US Environmental Protection Agency (EPA) classifies it in group A (human carcinogen, with enough evidence obtained from epidemiological studies) and establishes a risk of cancer through oral exposure (EPA, 2017; IARC, 2012). A number of studies have shown that intake of InAs can increase the risk of developing cancer of lung (Hubaux et al., 2013), skin (Bailey et al., 2009), bladder (Bailey et al., 2012), liver (Sung et al., 2012) and kidney (Yuan et al., 2010), among others.
Based on the fact that arsenic is one of the most dangerous trace elements for human health, in 2009 the European Food Safety Authority (EFSA) re-evaluated the toxicity and the health effects of InAs. According to human lung cancer data, the EFSA proposed to use the lowest limit of the 95 percentile of the experimental dose, associated with a 1% of incidence or extra risk (BMDL01). As a result, a range from 0.3 to 8.0 μg/kg body weight/day was set (EFSA, 2014). In 2010, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) established a BMDL0.5 of 3 μg/kg body weight/day (with an interval between 2 and 7 μg/kg body weight/day). Moreover, the provisional tolerable weekly intake (PTWI) established for InAs of 15 μg/kg body weight/week was withdrawn (FAO/WHO, 2010).
The last total diet study (TDS) conducted in Catalonia (Spain) in 2017 showed that rice is one of the food groups containing the highest concentrations of arsenic and InAs (González et al., 2019). However, it is hereby hypothesized that even though rice and rice-derived products are highly consumed, they might not pose a risk for human health. Since the content of organic and InAs in rice and rice products might vary, the Catalan Agency of Food Safety (ACSA) has launched a study aimed at: i) determining the concentration of this toxic trace element in these foodstuffs; ii) evaluating the exposure and the potential risks for the children and the adult population.
Section snippets
Sampling
In September 2018, rice and rice products were purchased in different stores located in Reus and Tarragona (Catalonia, Spain). Rice samples counted with 7 rice varieties: white long rice from Spain; white long rice from Asia (India/Pakistan); white round rice from Spain; white round rice from Asia (Japan); brown long rice from Spain; brown long rice from Asia (India/Pakistan) and brown round rice from Spain. Pre-cooked rice was also included, but a geographical differentiation was not
Results and discussion
Mean concentrations of total As and InAs are summarized in Table 2. In general, brown varieties of rice contained higher concentrations of total As and InAs than white rice. Specifically, the highest levels of total As and InAs were found in the brown round rice from Spain (229 and 190 μg/kg, respectively). This difference between brown and white rice is most probably due to the removal of the bran during the polishing of white rice, where most of the arsenic is accumulated. These findings are
Conclusions
In this study, the concentrations of total As and InAs in rice and rice-based products, as well as the dietary exposure considering different population groups and exposure scenarios, have been assessed. Brown varieties of rice presented higher concentrations of total As and InAs than white rice varieties, being the variety “brown, round rice from Spain” the one with the highest concentration of total As and InAs. In general, Spanish rice contained more total As and InAs than Asian rice.
CRediT authorship contribution statement
Neus González: Data curation, Formal analysis, Investigation, Software, Writing - original draft, Writing - review & editing. Josep Calderón: Formal analysis, Methodology, Writing - original draft, Writing - review & editing. Antoni Rúbies: Formal analysis, Methodology, Writing - original draft. Jaume Bosch: Conceptualization, Validation, Writing - original draft. Isabel Timoner: Validation, Writing - original draft. Victòria Castell: Conceptualization, Funding acquisition, Supervision, Writing
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This study was financially supported by the Catalan Food Safety Agency (ACSA), Department of Health, Generalitat de Catalunya, Barcelona, Catalonia, Spain.
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