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. 2011:1:72.
doi: 10.1038/srep00072. Epub 2011 Aug 23.

Maize grain and soil surveys reveal suboptimal dietary selenium intake is widespread in Malawi

Allan D C Chilimba  1 , Scott D Young, Colin R Black, Katie B Rogerson, E Louise Ander, Michael J Watts, Joachim Lammel, Martin R Broadley
Affiliations

Maize grain and soil surveys reveal suboptimal dietary selenium intake is widespread in Malawi

Allan D C Chilimba et al. Sci Rep. 2011.

Abstract

Selenium is an essential element in human diets but the risk of suboptimal intake increases where food choices are narrow. Here we show that suboptimal dietary intake (i.e. 20-30 µg Se person(-1) d(-1)) is widespread in Malawi, based on a spatial integration of Se concentrations of maize (Zea mays L.) grain and soil surveys for 88 field sites, representing 10 primary soil types and >75% of the national land area. The median maize grain Se concentration was 0.019 mg kg(-1) (range 0.005-0.533), a mean intake of 6.7 µg Se person(-1) d(-1) from maize flour based on national consumption patterns. Maize grain Se concentration was up to 10-fold higher in crops grown on soils with naturally high pH (>6.5) (Eutric Vertisols). Under these less acidic conditions, Se becomes considerably more available to plants due to the greater solubility of Se((IV)) species and oxidation to Se((VI)).

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Conflict of interest statement

Yara GmbH provided most of the funding for this study and has also funded other work in the groups of MRB/ADCC/SDY in the UK and Malawi. With the exception of JL, none of the authors of this study has received personal remuneration from Yara, nor do they own stock in the company. There are no other potential conflicts of interest.

Figures

Figure 1
Figure 1. Location of farmers' fields sampling sites in Malawi produced using ArcGIS (v. 9.3).
Figure 2
Figure 2. Concentrations of Se in maize grain (a) and soil (b,c) from farmers' fields surveys in Malawi.
Soil Se is expressed as total (b) and KH2PO4-extractable (c) Se forms. Data are presented on an Extension Planning Area (EPA) basis (mean ±s.e.m.). Note, total and KH2PO4-extractable soil Se data are missing for Chinguluwe EPA due to the loss of the soil sample. For Chitsime, Mbawa, and Ntonda EPAs there was insufficient soil sample remaining for KH2PO4-extractable Se to be analysed following other soil analyses.
Figure 3
Figure 3. Relationships between soil Se (total and KH2PO4-extractable forms) and soil pH, soil organic matter and maize grain Se concentration from a survey of farmers' fields in Malawi.
Figure 4
Figure 4. (a) Population distribution in Malawi at a District level.
Districts are numbered #1 (Balaka District) to #28 (Zomba District) as stated in Table 2 (NSO, 2008; ref. ; N.B. Neno District (#18) maps within Mwanza District (#16) and is not shown), (b) soil series maps based on ref. .Figure produced using ArcGIS (v. 9.3).
Figure 5
Figure 5. (a) Median grain Se concentrations on an Extension Planning Area (EPA) basis, (b) extrapolated grain Se concentration, based on median grain Se concentration for each soil type (two quintiles of grain Se concentration are not represented by median values for each soil type; these are labelled as n.d. in the inset key).
Figure produced using ArcGIS (v. 9.3).
See this image and copyright information in PMC

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