Arsenic is a widely-distributed toxic carcinogenic metalloid popularly known as the king of poisons and the poison of the kings. The history of intentional and accidental poisoning by arsenic dates back a long time.
Acute and long-term exposure of arsenic leads to several health problems and diseases in humans collectively referred to as “arsenicosis.” Arsenic exposure in pregnant women may also affect fetus development. Arsenic-related health effects include various skin related problems (hyperkeratosis, hyperpigmentation), cancer development in different tissues and organs (skin, bladder, kidney, lung), mee’s lines, and hair hypomelanosis.
The WHO has proposed Benchmark Dose Lower Limit (BMDL0.5) for arsenic that suggests a 0.5% increased incidence of cancer. These limits are 3 μg day−1 kg−1 bw, 5.2 μg day−1 kg−1 bw, and 5.4 μg day−1 kg−1 bw for lung cancer, bladder cancer, and skin lesions, respectively (WHO, 2011; JFCFA, 2011).
Both natural (biogeochemical) and anthropogenic activities are known to be the source of arsenic contamination in the environment. Severe arsenic contamination exists in Southeast Asian countries like Bangladesh, India, Pakistan, and China. In these regions, arsenic-contaminated groundwater is used as drinking water and also for irrigation purposes. This leads to arsenic entry into different crops and, subsequently, into the food chain through food grains, processed food items, vegetables, fruits, fish, mushrooms, etc.
Rice is known to be the most affected of all crops. The daily consumption of rice is very high in India, Bangladesh, as well as other Southeast Asian countries. These regions have severe and widespread arsenic contamination and are also the major rice-growing areas. Thus, arsenic contamination of groundwater and rice becomes a huge problem in these regions. However, it must be understood that the problem of arsenic accumulation in rice plants is of global concern, as rice import and export among different countries is a regular practice, and rice grains, rice milk, rice bran, and several rice-based food products are consumed by millions of people of different ages (from infants to adults), groups, and regions.
Researchers have focused on analyzing not only the whole rice grains but also a number of rice-based food products for arsenic levels and arsenic species. In addition, government agencies conduct an arsenic analysis of food items regularly. The results of hundreds of research articles and government reports have been eye-opening, as the presence of arsenic at higher-than-recommended levels has been detected in rice grains. Arsenic concentrations have been found to vary in different varieties of rice of varying origin, e.g. Indica vs. Japonica rice, local vs. high yielding varieties, long grain vs. short grain varieties, etc. Rice bran samples have also been found to contain a very high amount of arsenic (∼1 mg kg-1 dry weight; Sun et al., 2008) putting products using rice bran as an ingredient at risk. Different after-harvest treatments also affect arsenic concentrations in rice, for example, brown rice vs. parboiled brown rice and white rice vs. parboiled white rice (Batista et al., 2011).
Lately, there have been plenty of reports demonstrating arsenic presence in rice-based food products, including baby food items from different parts of the world. Hence, even the infants and toddlers are exposed to arsenic at a very young age (Carbonell-Barrachina et al., 2012; Cubadda et al., 2016). The problem is further exacerbated by the fact that infants and young children consume more food than adult people based on body weight. With rising concerns about arsenic in rice, the WHO has set a permissible limit for inorganic arsenic (arsenite + arsenate) of 0.2 mg kg-1 for white rice and 0.4 mg kg-1 for brown rice. The European Union (EU) prescribed the maximum limits for inorganic arsenic as 0.2 mg kg−1 for white rice and a limit of 0.1 mg kg−1 for rice-based food products for infants and young children.
With more and more research focused on evaluating the impact of arsenic contamination around the world, it has come to light that infiltration affects a number of crop plants (wheat, maize, burglar, pulses, beans etc.), fruits, vegetables (potato, lady finger, leafy vegetables etc.), mushrooms, and animal products (fish, meat, meat products, egg, milk, and dairy-based products). Because of this, arsenic consequently finds its way into commercial food products prepared from contaminated raw material (Zhao et al., 2010). Hence, the risk of As-exposure becomes pertinent not only to people living in arsenic-contaminated regions and/or consuming rice as major food but also to people living in other parts of the world. Future research needs to devise easy, low-cost methods for the routine sampling of water and food samples to ensure safe food for all.
The need was felt to devise the best possible low-cost method to reduce arsenic in rice grains purchased from the market. In this perspective, cooking methods have been researched to evaluate the impact of cooking on rice arsenic concentration and arsenic speciation. It has been found that the ratio of rice to water used for cooking of rice, water used for washing rice, the cooking duration, and the number of washing steps significantly influence the arsenic content and its bioaccessibility in cooked rice (Mwale et al., 2018; Rasheed et al., 2018).
Nonetheless, Gray et al. (2016) warned that if excess water is used for cooking rice, along with significant reduction in inorganic arsenic content, loss of nutrient elements like iron and vitamins (folate, thiamin, and niacin) might also occur. Hence, more research is needed to optimize a cooking method so as to achieve maximum possible arsenic reduction while managing the optimum nutritional quality of rice grains.
The years of research into arsenic in our food and drinking water have led not only to changes in arsenic limits (mentioned above) but also to changes in composition and types of infant and child food products. It has been found in a recent survey that the proportion of rice was varied while other grains (maize) were mixed in infant/baby food products in Ireland (Carey et al., 2018). In the future, strict regulations need to be imposed to make food items safe for consumption by people of all ages.
These findings are described in the article entitled A review of arsenic in crops, vegetables, animals and food products, recently published in the journal Food Chemistry. This work was conducted by Munish K. Upadhyay, Anurakti Shukla, Poonam Yadav, and Sudhakar Srivastava from Banaras Hindu University.
References:
- Batista, B. L., Souza, J. M. O., Souza, S. S., & Barbosa, J. (2011). Speciation of As in rice and estimation of daily intake of different As species by Brazilians through rice consumption. Journal of Hazardous Materials 191, 342–348. DOI: 10.1016/j.jhazmat.2011.04.087
- Carbonell-Barrachina, A. A., Wu, X., Ramirez-Gandolfo, A., Norton, G. J., Burlo, F., Deacon, C., et al. (2012). Inorganic As contents in rice-based infant foods from Spain, UK, China and USA. Environmental Pollution 163, 77 – 83. DOI: 10.1016/j.envpol.2011.12.036
- Carey, M., Donaldson, E., Signes-Pastor, A. J., & Meharg, A. A. (2018). Dilution of rice with other gluten free grains to lower inorganic arsenic in foods for young children in response to European Union regulations provides impetus to setting stricter standards. PloS One e0194700. DOI: 10.1371/journal.pone.0194700.
- Cubadda, F., D’Amato, M., Aureli, F., Raggi, A., & Mantovani, A. (2016). Dietary exposure of the Italian population to inorganic arsenic: The 2012−2014 total diet study. Food and Chemical Toxicology 98, 148−158. DOI: 10.1016/j.fct.2016.10.015
- Gray, P. J., Conklin, S. D., Todorov, T. I., & Kasko, S. M. (2016). Cooking rice in excess water reduces both As and enriched vitamins in the cooked grain. Food Additives and Contaminants: Part A 33, 78 – 85. DOI: 10.1080/19440049.2015.1103906
- JECFA (Joint FAO/WHO Expert Committee on Food Additives) (2011). Evaluation of certain contaminants in food. The seventy-second report, WHO, 1-115.
- Mwale, T., Rahman, M. M., & Mondal, D. (2018). Risk and benefit of different cooking methods on essential elements and arsenic in rice. International Journal of Environmental Research and Public Health, 15, 1056. DOI: 10.3390/ijerph15061056.
- Rasheed, H., Kay, P., Slack, R., & Gong, Y. Y. (2018). Arsenic species in wheat, raw and cooked rice: Exposure and associated health implications. Science of the Total Environment, 634, 366–373. DOI: 10.1016/j.scitotenv.2018.03.339.
- Sun, G. X., Williams. P. N., Carey, A. M., Zhu, Y. G., Deacon, C., Raab, A., et al. (2008). Inorganic As in rice bran and its products are an order of magnitude higher than in bulk grain. Environmental Science and Technology 42, 7542 – 7546. DOI: 10.1021/es801238p
- WHO (World Health Organization) (2011). Guidelines for drinking-water quality, vol. 4. pp. 315–318.
- Zhao, F. J., Stroud, J. L., Eagling, T., Dunham, S. J., McGrath, S. P., & Shewry, P. R. (2010). Accumulation, distribution, and speciation of As in wheat grain. Environmental Science and Technology 44, 5464-5468. DOI: 10.1021/es100765g