Elemental composition of Malawian rice
- 416 Downloads
Widespread potential dietary deficiencies of calcium (Ca), iron (Fe), iodine (I), selenium (Se) and zinc (Zn) have been identified in Malawi. Several deficiencies are likely to be compounded by high phytic acid (PA) consumption. Rice (Oryza sativa) is commonly consumed in some Malawian populations, and its mineral micronutrient content is important for food security. The considerable irrigation requirements and flooded conditions of paddy soils can also introduce or mobilise potentially toxic elements including arsenic (As), cadmium (Cd) and lead (Pb). The aim of this study was to determine the mineral composition of rice sampled from farmers’ fields and markets in Malawi. Rice was sampled from 18 extension planning areas across Malawi with 21 white (i.e. polished) and 33 brown samples collected. Elemental composition was determined by inductively coupled plasma-mass spectrometry (ICP-MS). Arsenic speciation was performed using high-performance liquid chromatography (HPLC)-ICP-MS. Concentration of PA was determined using a PA-total phosphorus assay. Median total concentrations (mg kg−1, dry weight) of elements important for human nutrition in brown and white rice, respectively, were: Ca = 66.5 and 37.8; Cu = 3.65 and 2.49; Fe = 22.1 and 7.2; I = 0.006 and <0.005; Mg = 1130 and 265; Mn = 18.2 and 9.6; Se = 0.025 and 0.028; and Zn = 17.0 and 14.4. In brown and white rice samples, respectively, median PA concentrations were 5438 and 1906 mg kg−1, and median PA:Zn molar ratios were 29 and 13. Concentrations of potentially toxic elements (mg kg−1, dry weight) in brown and white rice samples, respectively, were: As = 0.030 and 0.006; Cd ≤ 0.002 and 0.006; Pb = 0.008 and 0.008. Approximately 95 % of As was found to be inorganic As, where this could be quantified. Malawian rice, like the more widely consumed staple grain maize, contains inadequate Ca, I, Se or Zn to meet dietary requirements. Biofortification strategies could significantly increase Se and Zn concentrations and require further investigation. Concentrations of Fe in rice grain varied greatly, and this was likely due to contamination of rice samples with soil. Risk of As, Cd or Pb toxicity due to rice consumption in Malawi appears to be minimal.
KeywordsArsenic Micronutrient deficiencies Phytic acid Rice Selenium Zinc
EJMJ, MRB, ADCC, ELA, SDY and MJW conceived the study; EJMJ and ADCC collected samples; MJW and EMH analysed the samples; EJMJ drafted the text and figures; all authors read, contributed to and approved the final manuscript. EJMJ’s PhD studentship was funded by the University of Nottingham, UK and the British Geological Survey. The authors would like to thank Paul Williams (Queens University Belfast) and Andy Meharg (University of Aberdeen) for providing valuable advice, references and supplementary data during the manuscript drafting.
- Adedire, C. O., Adeyemi, J. A., Paulelli, A. C., Martins-Junior, A. C., Ileke, K. D., Segura, F. R., et al. (2015). Toxic and essential elements in Nigerian rice and estimation of dietary intake through rice consumption. Food Additives & Contaminants: Part B, 8(4), 271–276.Google Scholar
- Al-Rmalli, S. W., Jenkins, R. O., Watts, M. J., & Haris, P. I. (2012). Reducing human exposure to arsenic, and simultaneously increasing selenium and zinc intake, by substituting non-aromatic rice with aromatic rice in the diet. Biomedical Spectroscopy and Imaging, 1(4), 365–381.Google Scholar
- Banerjee, M., Banerjee, N., Bhattacharjee, P., Mondal, D., Lythgoe, P. R., Martinez, M., et al. (2013). High arsenic in rice is associated with elevated genotoxic effects in humans. Scientific Reports, 3, 1–8.Google Scholar
- Bohn, T., Davidsson, L., Walczyk, T., & Hurrell, R. F. (2004). Phytic acid added to white-wheat bread inhibits fractional apparent magnesium absorption in humans. American Journal of Clinical Nutrition, 79(3), 418–423.Google Scholar
- Broadley, M. R., Chilimba, A. D. C., Joy, E. J. M., Young, S. D., Black, C. R., Ander, E. L., et al. (2012). Dietary requirements for magnesium but not calcium are likely to be met in Malawi based on national food supply data. International Journal for Vitamin and Nutrition Research, 82(3), 192–199.CrossRefGoogle Scholar
- Daum, D., Bogdan, K., Schenk, M. K., & Merkel, D. (2002). Influence of the field water management on accumulation of arsenic and cadmium in paddy rice. In W. J. Horst, et al. (Eds.), Plant nutrition (pp. 290–291). Dordrecht: Springer.Google Scholar
- Duxbury, J. M., Mayer, A. B., Lauren, J. G., & Hassan, N. (2003). Food chain aspects of arsenic contamination in Bangladesh: Effects on quality and productivity of rice. Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances & Environmental Engineering, 38(1), 61–69.CrossRefGoogle Scholar
- Food and Agriculture Organization of the United Nations, FAO. (2015). FAOSTAT database. http://faostat3.fao.org/. Accessed June 2015.
- Gibson, R. S., Bailey, K. B., Gibbs, M., & Ferguson, E. L. (2010). A review of phytate, iron, zinc, and calcium concentrations in plant-based complementary foods used in low-income countries and implications for bioavailability. Food and Nutrition Bulletin, 31(2 Suppl), S134–146.CrossRefGoogle Scholar
- Gibson, R. S., Wawer, A. A., Fairweather-Tait, S. J., Hurst, R., Young, S. D., Broadley, M. R., et al. (2015). Dietary iron intakes based on food composition data may underestimate the contribution of potentially exchangeable contaminant iron from soil. Journal of Food Composition and Analysis, 40, 19–23.CrossRefGoogle Scholar
- Institute of Medicine of the National Academies, IOM. (2000). Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium and zinc. Washington DC: National Academies Press.Google Scholar
- Institute of Medicine of the National Academies, IOM. (2002). Dietary reference intakes for vitamin C, vitamin E, selenium, and carotenoids. Washington DC: National Academies Press.Google Scholar
- Kalimbira, A. A., Chilima, D. M., Mtimuni, B. M., & Mvula, N. (2005). Knowledge and practices related to use of iodised salt among rural Malawian households. Bunda Journal of Agriculture, Environmental Science and Technology, 3, 73–82.Google Scholar
- National Statistics Office of the Republic of Malawi, NSO. (2012). Malawi Third Integrated Household Survey (IHS3). NSO, Zomba, Malawi and World Bank Living Standards and Measurements Surveys. http://www.worldbank.org/en/research. Accessed Sep 2013.
- Pinson, S. R. M., Tarpley, L., Yan, W., Yeater, K., Lahner, B., Yakubova, E., et al. (2014). Worldwide genetic diversity for mineral element concentrations in rice grain. Crop Science, 55(1), 1–18.Google Scholar
- Reason, D. A., Watts, M. J., Devez, A., Broadley, M. R. (2015). Quantification of phytic acid in grains, British Geological Survey Open Report, OR/15/070, p. 18.Google Scholar
- Siyame, E. W. P., Hurst, R., Wawer, A. A., Young, S. D., Broadley, M. R., Chilimba, A. D. C., et al. (2013). A high prevalence of zinc-but not iron-deficiency among women in rural Malawi: A cross-sectional study. International Journal for Vitamin and Nutrition Research, 83(3), 176–187.CrossRefGoogle Scholar
- United States Department of Agriculture, Agricultural Research Service, USDA-ARS. (2013). USDA National Nutrient Database for Standard Reference, Release 26. http://www.ars.usda.gov/nutrientdata. Accessed Sep 2014.
- United States Environmental Protection Agency, US EPA. (1994). Integrated risk information system (IRIS): Cadmium. http://www.epa.gov/iris/subst/0141.htm. Accessed Sep 2015.
- United States Environmental Protection Agency, US EPA. (1998). Integrated risk information system (IRIS): Inorganic arsenic. http://www.epa.gov/iris/subst/0278.htm. Accessed Sep 2015.
- United States Food and Drug Administration, US FDA. (2013). Analytical results from inorganic arsenic in rice and rice products sampling. http://www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm319870.htm. Accessed Mar 2014.
- Verduzco‐Gallo, I., Ecker, O., & Pauw, K. (2014). Changes in food and nutrition security in Malawi: Analysis of recent survey evidence. Working Paper 06. International Food Policy Research Institute, Washington DC, USA.Google Scholar
- World Health Organization and Food and Agriculture Organization of the United Nations, WHO & FAO. (2004). Vitamin and mineral requirements in human nutrition. Geneva: WHO.Google Scholar
- World Health Organization, WHO. (2001). Arsenic and arsenic compounds. Environmental health criteria 224 (2nd ed.). Geneva: WHO.Google Scholar
- World Health Organization, WHO. (2008). Worldwide prevalence of anaemia 1993–2005: WHO global database on anaemia. Geneva: WHO. http://apps.who.int/iris/bitstream/10665/43894/1/9789241596657_eng.pdf. Accessed 19 July 2016.