The gastric bioaccessibility of Pb was investigated in soils and sediments from five villages in the Anka area of north-western Nigeria which has been adversely affected by artisanal mining of gold from lead-rich ores. In vitro bioaccessibility experiments were used to determine the extractability of Pb in order to evaluate the human health risk, especially to children below the age of five. The concentration of Pb in the simulated gastric fluids ranges from ~ 198 to 41740 µg, with corresponding human bioaccessible fraction between ~ 29 and 100% (mean, ~ 60%). Chemical daily intake (CDI, µg/Kg/Day) values of between 111 and 41587 are generally very high compared to the tolerable daily intake (TDI) of ~ 3.6 µg Pb/Kg/Day. The high bioaccessibility is a result of high total concentration of Pb and the presence of highly soluble carbonate and oxide minerals in the ores. These results point to the very adverse health effects likely to result from incidental hand-to-mouth ingestion of soils by children in the affected villages. The results further show that the low pH of gastric juices enhances the extraction of Pb. Given the likelihood of sub-nutrition in the affected communities, characterized by skipping of meals, which can result in lowering of the pH over extended periods, the risk of Pb poisoning is further increased. This study was based on a hand-to-mouth ingestion scenario alone, but as other exposure routes, such as eating improperly washed vegetables and inhalation of dust are possible, the risk might even be higher. This, along with the fate of extracted Pb in the intestinal environment may need to be evaluated in order to fully quantify the bioavailability of Pb in the area.

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The geology and groundwater condition of the area was studied with the aim of understanding their impact on the instability of the road in the study area. These include the petrology, geophysics and groundwater fluctuation (percentage in water table fluctuation). The methodology included geological field mapping, thin section preparation, resistivity and water table monitoring in dry and wet seasons. The study reveals that the road is underlain by schist, amphibolites and poorly fractured granite with quartz, biotite, hornblende and muscovite as the constituent minerals. The rocks have been altered through weathering to clayey minerals with resistivity values as low as 14 Ohm with the depth of weathering as high as 20 meter especially in the schist. The percentage of groundwater variation ranges between 154% and 2400% indicating medium to very high percentage of variation of groundwater fluctuation. These clay minerals absorb water and swell during the raining season and dry during the dry season. The result is the instability of the road pavement especially within the schist and where the elevation is lower. Proper design of the road and the provision of good drainage that will reduce the ingress of water are advised.

A field mapping and laboratory study was undertaken to characterize the lower portion of Bida Formation around Jima and Doko areas near Bida, central Nigeria. Field mapping revealed four lithofacies for the sandy braided river deposits. They are: (1) lithofacies Fa consists of gravely, very coarse sandstones; (2) lithofacies Fb is characterized by gravely, medium to very coarse grained sandstones; (3) lithofacies Fc is identified by coarse silt to fine grained sandstones; (4) lithofacies Fd is recognized by sheet-like beds of fine to medium grained sandstones. They record channel flow (Fa), subaqueous dune (Fb), overbank (Fc) and crevasse splay deposits (Fd) respectively. The four lithofacies allowed the definition of two architectural elements: (1) channel architectural element (CH) and (2) overbank architectural element (OF). A CH element overlain by an OF element defines a unit bar; while stacked, multiple CH overlain by an OF delineate a compound bar. Computation of grain size data for Fa and Fb facies yielded permeability values of 19.4 to 352.3 millidarcies using empirically generated equation. Because permeability values do not vary much, it is suggested that Fa and Fb be treated as one homogeneous entity if object based reservoir modelling of the sandstones is to be done. This work shows that detailed field mapping integrated with grain size data can offer valuable information useful for aquifer and reservoir studies of the sandstones.

Geotechnical tests were performed on granite and granite-gneiss rock samples of parts of Minna to know their suitability as construction aggregates. Eight rock samples were selected for porosity test, impact value, specific gravity and absorption capacity. The average porosity of the samples is 0.21, 0.12, 0.30, 0.10, 0.25, 0.25, 0.24 and 0.11 respectively for L1, L14, L15, L19, L21, L23, L25 and L29 which shows they are normal except L15 with a high porosity. Average impact value of the samples show they are suitable for wearing surface course in road and bridge construction, except samples L14 and L19 with average impact value of 32.8 and 34.9 respectively making them suitable only as bituminous macadam (maximum value = 35%). Sample L1 is not suitable as construction aggregates because it exceeds the maximum value specified for that purpose. The average specific gravity of the rocks are L1=2.68, L14=2.65, L15=2.65, L19=2.67, L21= 2.63, L23= 2.71, L25=2.65, and L29=2.69 respectively and which make them suitable as normal weight materials for construction. The average absorption capacity values of the rock samples are 0.20%, 0.20%, 0.50%, 0.10%, 0.25%, 0.10%, 0.50% and 0.20% respectively for samples L1, L14, L15, L19, L21, L23, L25, and L29. All testing followed the respective ASTM standards. Keywords: Geotechnical testing, construction aggregates, granite, granite-gneiss, Minna, Nigeria.