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.

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## Science in theNews

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

• Fertilizer usage and cadmium in soils, crops and food 2018-06-23

### Abstract

Phosphate fertilizers were first implicated by Schroeder and Balassa (Science 140(3568):819–820, 1963) for increasing the Cd concentration in cultivated soils and crops. This suggestion has become a part of the accepted paradigm on soil toxicity. Consequently, stringent fertilizer control programs to monitor Cd have been launched. Attempts to link Cd toxicity and fertilizers to chronic diseases, sometimes with good evidence, but mostly on less certain data are frequent. A re-assessment of this “accepted” paradigm is timely, given the larger body of data available today. The data show that both the input and output of Cd per hectare from fertilizers are negligibly small compared to the total amount of Cd/hectare usually present in the soil itself. Calculations based on current agricultural practices are used to show that it will take centuries to double the ambient soil Cd level, even after neglecting leaching and other removal effects. The concern of long-term agriculture should be the depletion of available phosphate fertilizers, rather than the negligible contamination of the soil by trace metals from fertilizer inputs. This conclusion is confirmed by showing that the claimed correlations between fertilizer input and Cd accumulation in crops are not robust. Alternative scenarios that explain the data are presented. Thus, soil acidulation on fertilizer loading and the effect of Mg, Zn and F ions contained in fertilizers are considered using recent $$\hbox {Cd}^{2+}$$ , $$\hbox {Mg}^{2+}$$ and $$\hbox {F}^-$$ ion-association theories. The protective role of ions like Zn, Se, Fe is emphasized, and the question of Cd toxicity in the presence of other ions is considered. These help to clarify difficulties in the standard point of view. This analysis does not modify the accepted views on Cd contamination by airborne delivery, smoking, and industrial activity, or algal blooms caused by phosphates.

• Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments 2018-06-23

### Abstract

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] − [AVS])/f oc , and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

• Cytotoxicity induced by the mixture components of nickel and poly aromatic hydrocarbons 2018-06-22

### Abstract

Although particulate matter (PM) is composed of various chemicals, investigations regarding the toxicity that results from mixing the substances in PM are insufficient. In this study, the effects of low levels of three PAHs (benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene) on Ni toxicity were investigated to assess the combined effect of Ni–PAHs on the environment. We compared the difference in cell mortality and total glutathione (tGSH) reduction between single Ni and Ni–PAHs co-exposure using A549 (human alveolar carcinoma). In addition, we measured the change in Ni solubility in chloroform that was triggered by PAHs to confirm the existence of cation–π interactions between Ni and PAHs. In the single Ni exposure, the dose–response curve of cell mortality and tGSH reduction were very similar, indicating that cell death was mediated by the oxidative stress. However, 10 μM PAHs induced a depleted tGSH reduction compared to single Ni without a change in cell mortality. The solubility of Ni in chloroform was greatly enhanced by the addition of benz[a]anthracene, which demonstrates the cation–π interactions between Ni and PAHs. Ni–PAH complexes can change the toxicity mechanisms of Ni from oxidative stress to others due to the reduction of Ni2+ bioavailability and the accumulation of Ni–PAH complexes on cell membranes. The abundant PAHs contained in PM have strong potential to interact with metals, which can affect the toxicity of the metal. Therefore, the mixture toxicity and interactions between diverse metals and PAHs in PM should be investigated in the future.