Banjul 2007

2rd Applied Geochemistry Symposium, Banjul,The Gambia, 10-15 Feb 2007

SELECTED PAPERS
BY JOSEPH BABADI JOHNS
1.Potential health risk in areas of high natural concentrations of thallium and importance of urine screening
The a lack of information in the literature regarding Tl exposure from naturally occurring Tl enrichment. This paper draws attention to the potential health risk posed by high concentrations of naturally occurring Tl in the environment. The inhabitants of a rural area in Bo Area of Sierra Leone, reside within a natural Tl accumulated environment resulting from Tl-rich sulfide mineralization, and they face ongoing severe Tl exposure. High Tl concentrations were detected in urine of the local residents. Urinary Tl concentrations are as high as 2668 ¨¬g/L, with most subjects surpassing the accepted world urinary Tl concentration at <1 ¨¬g/L for ˇ°non-exposedˇ± humans. The urinary Tl concentrations show significant differences among three communities (n = 21, p = 0.001), but no significant difference in either sex or age groups (n = 21, p = 0.7806). However, there is a positive statistical relationship between the extent of Tl exposure from Tl concentrations in soil and crops in the immediate environment and the concentrations of Tl detected in urine. A majority of the volunteer subjects from the communities have urinary Tl concentrations above 4.5¨C6 ¨¬g/L, implying early adverse health effects, and some of them have over 500 ¨¬g/L urinary Tl, considered to be at/about the level of clinical intoxication. This study has been able to identify that the elevated urinary Tl concentrations are mainly attributable to Tl accumulation in locally grown vegetables, which acquire Tl from the soil. This study also shows that Tl in urine of the local population represents a steady-state condition with long-term exposure, and that urinary Tl concentrations can be taken as a bio-marker of total dose based upon total daily dietary intake. This study demonstrates that natural sources of elevated Tl pose a potential health risk to the population, and that monitoring the urinary Tl concentration is a reliable and accurate way of bio-marking Tl exposure

2.BY MOUSSA BACHIR CISSOKO,DAVID BARROW AND JENNIFFER SAFFIE KANU
The purpose of this study was to examine the influence of parent sediment material on soil geochemistry and to locate possible pollution sources in the area of Freetown,Serria Leone. The study area is a terrain and subsurface samples were chosen to represent different parent sediment materials: till, fluvial or littoral sand, clay, peat and marine mud. Elemental concentrations of surface (100 samples) and background soil (50 samples) were analysed by ICP-AES (Al, Ba, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Sr, Ti, V) and by graphite furnace AAS (As, Cd, Mo, Se). Loss-on-ignition was determined as an indicator of organic matter. Analytical results were examined using multivariate statistical methods. The results indicate that the studied soils are not heavily contaminated; there were only few sample sites with elevated heavy metal concentrations. High Pb concentrations were observed along main traffic routes, and also in places where there has been small-scale use of antifouling paints. However, concentrations of heavy metals in topsoil were in general significantly lower than those measured in large cities elsewhere. The parent material strongly affects the geochemical character of the soils. Clays naturally have a significantly higher concentration of heavy metals than sands or till material. This is also reflected in concentrations in organic topsoil. When assessing target levels for polluted soil, the primary sediment appears to be a more important factor than the amount of organic matter.

CASE STUDY SIERRA LEONE JUNE 2005 Arsenic in groundwater from mineralised Proterozoic basement rocks of Sierra Leone.

Joseph Barbadi JOHNS(1) and Fatou Kinneh TRAWALLY(2)
1. Department of Geophysics and Resource Development
2. Department of Minerals, Water and Rural Development

This study describes the hydrogeochemistry and distributions of As in groundwater from a newly investigated area of Kagbere, Kabala District, Northern province of Sierra Leone. Groundwaters have been sampled from hand-pumped boreholes and dug wells close to the Kagbere, Kabala District, Northern province of Sierra Leone. Although most analysed groundwaters have As concentrations of less than 10 μg L−1, they have a large range from <0.5 to 1630 μg L−1. The highest concentrations are found in borehole waters; all dug wells analysed in this study have As concentrations of <10 μg L−1. Skin disorders (melanosis, keratosis and more rare skin tumour) have been identified among the populations in three villages in northern Sierra Leone, two within the study area. Although detailed epidemiological studies have not been carried out, similarities with documented symptoms in other parts of the world suggest that these are likely to be linked to high concentrations of As in drinking water. The high-As groundwaters observed derive from zones of Au mineralisation in Birimian volcano-sedimentary rocks, the Au occurring in vein structures along with quartz and altered sulphide minerals (pyrite, chalcopyrite, arsenopyrite). However, the spatial variability in As concentrations in the mineralised zones is large and the degree of testing both laterally and with depth so far is limited. Hence, concentrations are difficult to predict on a local scale. From available data, the groundwater appears to be mainly oxic and the dissolved As occurs almost entirely as As(V) although concentrations are highest in groundwaters with dissolved-O2 concentrations <2 mg L−1. The source is likely to be the oxidised sulphide minerals and secondary Fe oxides in the mineralised zones. Positive correlations are observed between dissolved As and both Mo and W which are also believed to be derived from ore minerals and oxides in the mineralised zones. The discovery of high As concentrations in some groundwaters from the Birimian rocks of northern Sierra Leone reiterates the need for reconnaissance surveys in mineralised areas of crystalline basement.

CASE STUDIES
download CASE STUDIES 1 download CASE STUDIES 2 download CASE STUDIES 3 download CASE STUDIES 4 download CASE STUDIES 5