SEGH Articles

Soil: an important part of a healthy diet?

20 May 2011
Iodine is essential for healthy human life, and is taken up by crops from the soil. However, current research shows that the soil itself has an important part to play in determining how much iodine reaches our food.

Iodine is essential for healthy human life, and insufficient intake can result in reduced mental and physical well-being. In some places, however, even when there is plenty of iodine present in soil, there is still a deficiency in food, crops and grazing pasture for livestock, with social and economic impacts for affected communities.

Cows rely on sufficient iodine intake from the pasture they graze, but in some areas require dietary supplements to maintain health.

A current Nottingham-based PhD project is focussing on how the interaction between soil and iodine affects the availability of iodine to plants, and hence how the soil influences the amount of iodine entering the food chain. Research is being carried out using soils from Northern Ireland, mainly from pasture sites, to investigate how iodine, washed into soil by rain, behaves when it comes into contact with the earth: is it leached through the topsoil layer to depths inaccessible to roots? Is it locked away onto solid soil particles? Does it stay within the soil moisture, to potentially be taken up by plants? Current understanding is that all of these scenarios occur to some extent, and the properties of the individual soil determine ultimately how much iodine is taken up by the plants growing on it.

Soils have a range of properties including texture and composition which affect how iodine behaves once it is in contact with them.

A map of total soil iodine concentrations in Northern Ireland has recently been produced by the Geological Survey of Northern Ireland as part of the Tellus project (Smyth, D. and C. C. Johnson (2011). "Distribution of iodine in soils of Northern Ireland." Geochemistry-Exploration Environment Analysis 11(1): 25-39). Interpretation of the map revealed that although iodine concentrations in surface soils of Northern Ireland are generally high (on average around 10 mg kg-1), the concentration range was large (0.5 - 600 mg kg-1) and depended strongly on the characteristics of the soil. Soils rich in organic matter (e.g. peat) tended to retain most iodine. Additionally, a coastal fringe of particularly high iodine concentrations was identified and linked to relatively high marine concentrations of iodine. Within the last decade the British Geological Survey (BGS) has investigated the concentration of iodine in soils around the world, including in China, Morocco and Argentina. These projects have confirmed that low soil iodine concentration can result in whole communities being affected by iodine deficiency diseases, but have also shown that iodine deficiency can be a problem in areas where soil iodine concentration is not particularly low.  


This PhD research, jointly sponsored by the University of Nottingham and the BGS University Funding Initiative, builds on existing knowledge of iodine concentration in soils of Northern Ireland and looks deeper into how soil itself can affect the availability of iodine and why the problem does not occur everywhere. The ultimate aim is to create a computer model to predict where iodine deficiency diseases are likely to occur, allowing intervention measures to be planned for the places where they are most needed.


Soil and grass samples were collected in Northern Ireland...





...where careful recording of soil properties including colour and texture was required.



For further information about this project, please email Hannah Smith on

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