Heavy Metal Pollution of Natural Waters in Abakaliki, Ebonyi State, Nigeria

Abakaliki is one of the fast growing cities of South Eastern Nigeria. It depends mainly on surface water and limited groundwater supplies from a highly jointed and weathered shale-regolith aquifer. Since the aquifer is lithologically similar to a Nigerian rock formation that has been established as having groundwater - laden with heavy metals, the waters from the shale-regolith aquifer was tested for its heavy metal status. A few hand- dug wells and streams were also tested since they are hydraulically connected to the same aquifer. A total of 20 water samples were tested for their concentration levels with respect to iron (Fe), lead (Pb), copper (Cu), zinc (Zn), cadmium (Cd) and arsenic (As). Concentration levels for copper (Cu) and zinc (Zn) were below maximum contaminant levels (MCL) but iron (Fe) ranges from 0.2mg/l to 9.2mg/l. Its average value (5.44mg/l) exceeds the MCL by 18 times. The range for lead (Pb) is from BDL (below detection limits) to 13.8mg/l which exceeds the prescribed limits by 300 times. Cadmium (Cd) ranges from BDL to 0.67mg/l while arsenic levels vary from 0.1mg/l to 2.9mg/l. Their average values exceed prescribed limits by 50 and 159 times respectively. Mobilization of these heavy metals into natural water seem to be enhanced by iron oxyhydroxide reduction and nitrate reduction in processes that are microbially-driven. Health risks of the continued exposure of the Abakaliki population to these heavy metals is potentially serious.