SEGH Articles

# Geochemistry in Africa

26 January 2017

Michael Watts and Elliott Hamilton returned to Africa to undertake two main tasks; (1) find a conference venue for the Society for Environmental Geochemistry 2018 international conference to be hosted in Victoria Falls, and (2) undertake fieldwork in the Zambian copperbelt as part of the Royal Society-DFID project (Royal Society-DFID project).

We met up with Dr Godfrey Sakala (Zambian Agriculture Research Institute) and Professor Florence Mtambanengwe (University of Zimbabwe) in Victoria Falls and viewed venues for hosting 150-200 people.  The location is ideally suited, with ample accommodation, conference facilities, transport connections, activities, is safe to walk around and of course the spectacle of Victoria Falls. The Falls are a must see and a gentle introduction to Africa for the uninitiated, with many National Parks close by in Zimbabwe, Zambia and Botswana.  A video was filmed to begin the promotion of the conference and signpost SEGH 2018 VicFalls which will appear on  http://segh.net/events/  shortly.

We moved onto Zambia with Dr Sakala and headed up to Kitwe in the Copperbelt to join Prof. Maseka from the Copperbelt University to follow up on previous field collections in Mugala village where field characterisation identified specific plots for experimental trials to investigate the influence of soil management strategies, such as organic incorporation, liming, low tillage (Conservation Agriculture) on the uptake of metals deposited through dust onto agricultural soils from nearby mine tailings.  Elliott Hamilton will explain more in a follow-up blog about his PhD and some of the findings so far.  Belinda Kaninga, one of our Royal Society-DFID PhD students has set out her first season field experiments as identified by the site characterisation and will bring the resultant soil and crop samples to BGS for analysis next May.

Both Elliott and Belinda are using the same location for experimental trials, with Elliott focussing on the control parameters for Chromium (Cr) soil-to-crop transfer employing elemental speciation and isotope dilution for pot experiments using soil samples collected on this visit across the range of Cr concentrations and soil pH identified. These experiments will be undertaken at Sutton Bonington campus (University of Nottingham).  The processing of samples back in ZARI also allowed us to work with lab staff, review training needs and preparations for our upcoming purchase of Microwave-Plasma Atomic Emission Spectrometers in each of Malawi, Zambia and Zimbabwe. Meanwhile, Belinda is investigating a broad panel of metals (Pb, Cu, Zn, Cd, Mn, Al, Ni) and the application of specific Conservation Agriculture methodologies and potential influence on the availability of metals for soil-to-plant uptake.  Belinda has conducted pot trials at the ZARI research station in Lusaka, but as mentioned, recently set up her field plots in collaboration with the village chief and local farmers which will run over two growing seasons.

A further project was initiated with Prof. Maseka and Dr Sakala to investigate the potential exposure to metals from dust inhalation from the Mugala mine tailings in the nearby village, comparing pathways of exposure from environmental samples through to biological samples from a biomonitoring collection (urine, blood).  The focus of the project will be a two-year MSc project undertaken by Lukundo Nakaona, in collaboration with the CBU Department for Environmental and Agricultural Sciences and Medical School, ZARI and BGS-UoN (CEG).  There are many other possibilities for environmental-health exposure and food security studies with our close partners at ZARI, CBU and UNZA (University of Zambia).  In particular, scope for GCRF proposals to provide capacity strengthening in technical capability to cement the strong scientific activities of our partners both in Zambia, the wider Royal Society-DFID network in Zimbabwe and Malawi and with other partners in Kenya and Tanzania.

By Michael Watts, Elliott Hamilton, Belinda Kaninga, Kenneth Maseka and Godfrey Sakala

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## 34th SEGH International Conference: Geochemistry for Sustainable Development

Victoria Falls, Zambia

02 July 2018

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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.