SEGH Articles

Notes from Malawi

07 November 2012
Plant and crop selenium concentration shows strong geochemical control, and our data suggests widespread high prevalence of dietary Se deficiency across Malawi, primarily due to the low pH of the predominant soil types causing Se to be held in an unavailable form.

 As previously documented on this website 

(http://segh.net/articles/Ecosystem_services_to_alleviate_micronutrient_malnutrition_in_Sub_Saharan_Africa/), the British Geological Survey (BGS), the University of Nottingham (UoN) and the Malawian Ministry of Agriculture are working to improve 

understanding of mineral intake levels in Malawi and explore options for addressing deficiencies. Plant and crop selenium (Se) concentration shows strong geochemical control, and our data suggests widespread high prevalence of dietary Se deficiency across Malawi, primarily due to the low pH of the predominant soil types which causes Se to be held in an unavailable form.

Selenium is only required in very small quantities – the daily dietary requirement for the whole population of Africa is around 50kg. One option would be to supplement fertilisers with tiny amounts of Se, a policy that was adopted in Finland in the 1980s. Our field trials in Malawi have shown this to be potentially effective in raising maize grain Se levels (Chillimba et al. 2011). Wider testing is now required considering the variety of cropping systems found around the country, and that many farmers are unable to afford fertiliser.Malawian Ministry of Agriculture are working to improve the understanding of mineral intake levels in Malawi and explore options for addressing deficiencies. Plant and crop selenium (Se) concentration shows strong geochemical control, and our data suggests widespread high prevalence of dietary Se deficiency across Malawi, primarily due to the low pH of the predominant soil types which causes Se to be held in an unavailable form.

Another option is liming, which I will be testing with maize field trials this year at three locations in central and northern Malawi.  By increasing soil pH, liming has the potential to improve Se availability and hence increase plant uptake.  Liming might also provide economic benefits to farmers. A BGS-led study in Zambia (FarmLime) showed that liming rates around 0.5-1 tonne per hectare can increase maize and groundnut yields, with a positive cost-benefit ratio. However, the affordability and availability of lime depends greatly on proximity to the lime source, and many farmers struggle to afford inputs due to lack of credit. In addition, we expect that improvements in grain Se content might only be seen at much higher levels of liming.

Finally, we are exploring options for meeting dietary requirements of Se (and many other minerals, including calcium, iodine and zinc) through dietary diversification. In order to help inform this study, I have been busy collecting food samples from around Malawi which will be shipped back to the UK and analysed at BGS and UoN for mineral content. At this time of year, near the end of the dry season, most households are relying on grain stocks from May’s harvest. This means maize for most, although pearl millet and sorghum are preferred in the Shire valley in the south due to their drought tolerance. Grain is generally milled at local mills and boiled in water to prepare a thick porridge, which is accompanied by a “relish” of boiled leaves, beans, or sometimes fish from Lake Malawi. Most households collect vegetable leaves during the rainy season (including pumpkin leaves, bean leaves and the leaves of many different indigenous vegetables such as “chisoso” and “tove”), with some cooked fresh and some sun-dried in order to have supplies through the dry season. For all food samples collected, we also take a coupled soil sample. This will help to identify the influence of soil geochemistry on crop mineral content.

The planting rains are due soon, working their way up from the south, and farmers are busy preparing their maize ridges with hand hoes. It’s an exciting time of year, though slightly nail-biting as planting too early or too late can lead to crop failure. Farmers around Mzuzu where I am staying have found climate change, especially unpredictable rainfall patterns, a major challenge in recent years. Their anecdotal evidence of a warming climate and shorter rains fits with empirical data (http://mtc-m17.sid.inpe.br/col/sid.inpe.br/mtc-m17@80/2006/11.27.17.33/doc/Coelho.Evidence.pdf ).

 
 
All our fieldwork is done through the Malawi Ministry of Agriculture. As well as the obvious advantages garnered through local knowledge, contacts and resources, the setup also provides a route for information dissemination through the agricultural extension offices, a major source of support for most farmers.

Conducting research in Malawi does throw up some logistical difficulties, such as the fairly frequent fuel shortages. But in a country where the majority of people are involved in agriculture, mainly for subsistence, and where many households are just one poor harvest away from hunger, agricultural research can greatly help farmers through provision of information. Particularly in a subsistence context and given Malawi’s health and nutrition indicators (such as almost half children under five years of age are medically classed as “wasted”, and almost half non-pregnant women aged 15-49 are anaemic), agricultural policy and interventions need to aim for nutritional benefits, not just focus on yields.

Edward Joy

University of Nottingham – British Geological Survey – Ministry of Agriculture, Malawi.

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. http://www.nature.com/srep/2011/110823/srep00072/full/srep00072.html

Keep up to date

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

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

  • Improving arsenopyrite oxidation rate laws: implications for arsenic mobilization during aquifer storage and recovery (ASR) 2018-04-25

    Abstract

    Aquifer storage and recovery (ASR) and aquifer recharge (AR) provide technical solutions to address water supply deficits and growing future water demands. Unfortunately, the mobilization of naturally present arsenic due to ASR/AR operations has undermined its application on a larger scale. Predicting arsenic mobility in the subsurface during ASR/AR is further complicated by site-specific factors, including the arsenic mobilization mechanisms, groundwater flow conditions, and multi-phase geochemical interactions. In order to ensure safe and sustainable ASR/AR operation, a better understanding of these factors is needed. The current study thus aims to better characterize and model arsenic remobilization at ASR/AR sites by compiling and analyzing available kinetic data on arsenic mobilization from arsenopyrite under different aqueous conditions. More robust and widely applicable rate laws are developed for geochemical conditions relevant to ASR/AR. Sensitivity analysis of these new rate laws gives further insight into the controlling geochemical factors for arsenic mobilization. When improved rate laws are incorporated as the inputs for reactive transport modeling, arsenic mobilization in ASR/AR operations can be predicted with an improved accuracy. The outcomes will be used to guide groundwater monitoring and specify ASR/AR operational parameters, including water pretreatment requirements prior to injection.

  • Heavy metal exposure has adverse effects on the growth and development of preschool children 2018-04-25

    Abstract

    The purpose of this study was to investigate the associations between levels of lead (Pb), cadmium (Cd), chromium (Cr), and manganese (Mn) in the PM2.5 and blood and physical growth, and development parameters including birth length and weight, height, weight, body mass index (BMI), head circumference, and chest circumference in preschool children from Guiyu (e-waste exposure area) and Haojiang (the reference area). A total of 470 preschool children from Guiyu and Haojiang located in southeast coast of China were recruited and required to undergo physical examination and blood tests during the study period. Birth length and weight were obtained by birth records and questionnaire. Pb and Cd in both PM2.5 and blood were significantly higher in Guiyu than Haojiang. Remarkably, the children of Guiyu had significantly lower birth weight and length, BMI, and chest circumference when compare to their peers from the reference area (all p value < 0.05). Spearman correlation analyses showed that blood Pb was negatively correlated with height (r = −0.130, p < 0.001), weight (r = −0.169, p < 0.001), BMI (r = −0.100, p < 0.05), head circumference (r = −0.095, p < 0.05), and chest circumference (r = −0.112, p < 0.05). After adjustment for the potential confounders in further linear regression analyses, blood Pb was negatively associated with height (β = −0.066, p < 0.05), weight (β = −0.119, p < 0.001), head circumference (β = −0.123, p < 0.01), and chest circumference (β = −0.104, p < 0.05), respectively. No significant association between blood Cd, Cr, or Mn was found with any of our developmental outcomes. Taken together, lead exposure limits or delays the growth and development of preschool children.

  • Contamination characteristics of trace metals in dust from different levels of roads of a heavily air-polluted city in north China 2018-04-24

    Abstract

    Concentrations of eight trace metals (TMs) in road dust (RD) (particles < 25 μm) from urban areas of Xinxiang, China, were determined by inductively coupled plasma mass spectrometry. The geometric mean concentrations of Zn, Mn, Pb, As, Cu, Cr, Ni and Cd were 489, 350, 114, 101, 60.0, 39.7, 31.6, and 5.1 mg kg−1, respectively. When compared with TM levels in background soil, the samples generally display elevated TM concentrations, except for Cr and Mn, and for Cd the enrichment value was 69.6. Spatial variations indicated TMs in RD from park path would have similar sources with main roads, collector streets and bypasses. Average daily exposure doses of the studied TMs were about three orders of magnitude higher for hand-to-mouth ingestion than dermal contact, and the exposure doses for children were 9.33 times higher than that for adults. The decreasing trend of calculated hazard indexes (HI) for the eight elements was As > Pb > Cr > Mn > Cd > Zn > Ni > Cu for both children and adults.