The Biu Volcanic Province is one of the largest Volcanic Provinces in Nigeria covering an area
of 5000 km2 with a thickness of 250m. Geochemical analysis of the volcanic soil revealed the
complete leaching of the major elements (CaO K2O MgO MnO and TiO2) from the surface soil
probably into water sources. This may explain the extremely high Ca and K levels especially in
the stream water where they display values of 348mg l and 36 mg l as against 200mg l to 12 mg l
respectively of WHO admissible limits for drinking water. The accumulation of transition metals
in the soil (Co 84-111ppm Cr: 230-441ppm) Ni: 169-237ppm) is geogenic derived from the
weathering of the host basaltic rock. Cr Ni and Cu do not easily form soluble ions in
solution explaining why they display lower levels below their respective WHO admissible limits
for drinking water. The absence in the soil profile and the extremely higher values of
potentially harmful elements (PHEs) (As Se Sb and Pb) in the spring and stream water as
opposed to the lower values in the wells and borehole water suggest their extreme solubility
direct leaching and transportation of these elements from the surrounding rocks into the
surface water which may be source of exposure to the inhabitants.
