SEGH Articles

Is there an environmental link to esophageal cancer in Tanzania?

07 July 2015
Scientists from the Centre for Environmental Geochemistry are helping health organisations understand why esophageal cancer is localised within specific areas of the African Rift Valley. Whilst various causal factors are now under investigation, such as high-strength kill-me-quick alcohol consumption or hot tea drinking, it is difficult to fully explain the localised nature of the burden. Here Dr Michael Watts outlines why soil around Mount Kilimanjaro could unearth some answers.

Dr Valerie McCormack from the International Agency for Research on Cancer (IARC, part of the World Health Organisation) has studied the high prevalence of esophageal cancer in the Rift Valley and identified a particularly localised incidence of cases in the Mount Kilimanjaro area of Tanzania. A hypothesis was presented that an environmental factor, such as exposure to potentially harmful elements or organics (e.g. polycyclic aromatic hydrocarbons, PAHs, from wood fires) or deficiency of essential micronutrients (e.g. zinc) that diminishes the body’s ability to recover from or buffer an event that may cause cell damage, could be contributing to this.

Kilimanjaro District

This is where the skills of the Centre for Environmental Geochemistry (CEG) team come in. The BGS Inorganic Geochemistry team assisted IARC-WHO and the Kilimanjaro Christian Medical Centre (KCMC) in designing and undertaking a detailed survey of soil, water and crop samples in the Kilimanjaro district.

Children in Masame

Our primary aim was to link geochemistry and crop data with areas in which esophageal cancer cases were prevalent.  In addition, the data will demonstrate a spatial understanding of the geochemistry of the differing climatic zones and food production areas around Mount Kilimanjaro and to provide an indication of micronutrient composition or presence of potentially harmful elements.


This increased understanding of the soil and crops in Kilimanjaro will improve baseline evidence for a differing climatic zone compared to previous work in Sub-Saharan Africa (previous blogs), to inform future experimentation of agricultural methods that could improve soil-crop transfer of micronutrients for onward health benefits. 


We also provided training to local counterparts from KCMC and the Ministry of Agriculture Kilimanjaro District Extension Office in the collection of environmental samples, recording of field data for quality assurance / data management and onward presentation in GIS maps for agricultural planning tools. It is a privilege to be able to help where our skills are needed most and it’s clear these strong working relationships will bring benefits to local populations and the wider science community. We see clear opportunities for future collaboration with all of the partners we worked with in Tanzania, including the Regional Area Secretariat from the Prime Minister’s Office.

Rombo Mkuu

In fact the CEG has already partnered again with IARC-WHO (the project leaders) on a recently gained grant from the US National Cancer Institute to study a similarly high-localised prevalence of esophageal cancer in the Eldoret region of Kenya.  Such work involves the cross-disciplinary collaboration of epidemiologists, medics, health practitioners, biostatisticians, geochemists, farmers and local agricultural extension workers and commences 2015 to 2017. Watch out for future blogs and see all our research via our CEG website - 

Dr Michael Watts
Head of Inorganic Geochemistry, Centre for Environmental Geochemistry

Suggestions for further reading:

Joy et al. (2015). Zinc enriched fertilisers as a potential public health intervention in Africa, DOI:10.1007/s11104-015-2430-8. 

Gibson RS, Wawer AA, Fairweather-Tait SJ, Hurst R, Young SD, Broadley MR, Chilimba ADC, Ander EL, Watts MJ, Kalimbira A, Bailey KB, Siyame EWP. (2015). Dietary iron intakes based on food composition data may underestimate the contribution of potentially exchangeable contaminant iron from soil, Journal of Analytical Food Research (in press).

Joy, EJM, Broadley, MR, Young, SD, Black CR, Chilimba, ADC, Ander, EL, Barlow, TS and Watts, MJ*. (2015). Soil type influences crop mineral composition in Malawi, Science Total Environment, 505, 587-595.

Joy, E, Ander, EL, Young, SD, Black, C, Watts, MJ, Chilimba, ADC, Chilima, B, Siyame, E, Kalimbira, A, Hurst, R, Fairweather-Tait, SJ, Stein, A, Gibson, RS, White, P, Broadley, M. (2014) Dietary mineral supplies in Africa, Physiologia Plantarum, 151, 208-229.

Siyame E; Hurst R; Wawer AW;Young SD; Broadley MR; Chilimba ADC Ander EL; Watts MJ; Chilima B; Gondwe J; Kang’ombe D; Kalimbira A; Fairweather-Tait SJ; Bailey KB; Gibson RS. (2014). 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.

Hurst, R, Siyame, E, Young, SD, Chilimba, ADC, Joy, EJM, Black, CR, Ander, EL, Watts, MJ, Chilima, B, Gondwe, J, Kang’ombe, D, Stein, AJ, Fairweather-Tait, SJ, Gibson, R, Kalimbira, A, Broadley, MR*. (2013). Soil-type influences human selenium status and underlies widespread selenium deficiency risks in Malawi, Scientific Reports, 3, 1425.

Broadley MR, Chilimba ADC, Joy, E, Young SD, Black CR, Ander EL, Watts MJ, Hurst R, Fairweather-Tait SJ, White PJ, Gibson RS. (2012). Dietary requirements for magnesium but not calcium are likely to be met in Malawi based on national food supply data, International Journal of Vitamin and Nutrition Research, 82(3), 192-199.

Joy EJM, Young SD, Black CR, Ander EL, Watts MJ and Broadley MR. (2012). Risk of dietary magnesium deficiency is low in most African countries based on food supply data, Plant and Soil, 368. 129-137.

W H Shetaya, S D Young, M J Watts, E L Ander and E H Bailey (2012). Iodine dynamics in soils, Geochemica et Cosmochimica Acta, 77, 457 – 473.
Chilimba, A.D.C., Young, S.D., Black, C.R., Ander, E.L., Watts, M.J., Lammel, J. and 

Broadley, M.R. (2011). Maize grain and soil surveys reveal suboptimal dietary selenium intake is widespread in Malawi, Scientific Reports, 1, 1 - 9.



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

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


    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


    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.