title: Elemental composition of Malawian rice.
abstract: 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.
authors.affiliation: Department of Population Health, London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.|Inorganic Geochemistry, Centre for Environmental Geochemistry, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK.|School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, LE12 5RD, UK.
authors.forename: Edward J M
authors.initials: EJM
authors.lastname: Joy
authors.affiliation: Inorganic Geochemistry, Centre for Environmental Geochemistry, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK.
authors.forename: E
authors.initials: E
authors.lastname: Louise Ander
authors.affiliation: School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, LE12 5RD, UK.
authors.forename: Martin R
authors.initials: MR
authors.lastname: Broadley
authors.affiliation: School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, LE12 5RD, UK.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Young
authors.affiliation: Department of Agricultural Research Services, Ministry of Agriculture, Irrigation and Water Development, P.O. Box 30779, Lilongwe 3, Malawi.
authors.forename: Allan D C
authors.initials: ADC
authors.lastname: Chilimba
authors.affiliation: Inorganic Geochemistry, Centre for Environmental Geochemistry, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK.
authors.forename: Elliott M
authors.initials: EM
authors.lastname: Hamilton
authors.affiliation: Inorganic Geochemistry, Centre for Environmental Geochemistry, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK. mwatts@bgs.ac.uk.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Watts
mesh_terms: D001151:Arsenic / Q000008:administration & dosage / Q000633:toxicity; D002104:Cadmium / Q000032:analysis / Q000633:toxicity; D002118:Calcium / Q000032:analysis; D003300:Copper / Q000032:analysis; D003677:Deficiency Diseases / Q000209:etiology; D004602:Elements; D006801:Humans; D007455:Iodine / Q000032:analysis; D007501:Iron / Q000032:analysis; D007854:Lead / Q000032:analysis / Q000633:toxicity; D008274:Magnesium / Q000032:analysis; D008295:Malawi; D008345:Manganese / Q000032:analysis; D012275:Oryza / Q000737:chemistry*; D010833:Phytic Acid / Q000009:adverse effects / Q000032:analysis*; D012643:Selenium / Q000032:analysis; D012987:Soil; D012989:Soil Pollutants; D053719:Tandem Mass Spectrometry; D015032:Zinc / Q000032:analysis
chemical_list: D004602:Elements; D012987:Soil; D012989:Soil Pollutants; D002104:Cadmium; D007854:Lead; D008345:Manganese; D003300:Copper; D010833:Phytic Acid; D007455:Iodine; D007501:Iron; D012643:Selenium; D008274:Magnesium; D015032:Zinc; D001151:Arsenic; D002118:Calcium
keywords: Arsenic; Micronutrient deficiencies; Phytic acid; Rice; Selenium; Zinc