Elevated Concentration Levels of Heavy Metals in the Natural Waters of Awgu-Ndeabor Shales Aquifer, South-Eastern Nigeria

Abstract

The weathered horizon of Awgu-Ndeabor Shales is aquiferous. Lithologically the Awgu-Ndeabor Shales consist of grey shales, sandstones, siltones and occasional limestones. The weathered and fractured zone ranges from 30m-70m in thickness and supplies  ground water to about 8(eight) boreholes and the Umara spring in the study area. Major element concentrations in the groundwater system are all well below WHO or USEPA limits. Heavy metals that exceed prescribed limits include Arsenic (As) , Cadmium (Cd) and Lead(Pb). The average concentration for arsenic (As) and Cadmium are 31.993mg/ ? and 5.55mg/? which are more than 319 and 110times the Maximum Contaminant Levels (MCL) respectively. The lead (Pb) concentration has the average value of 128.44mg/ ? which is more than 8200 times the limit set by USEPA. These anomalous values pose serious health risks. The lead-zinc mineralization zone at Ishiagu which has a boundary with the study area and the host minerials in the Agwu-Ndeabor shales are probably responsible for this geogenic contamination of the water system.

Keywords: Geogenic, Awgu- Ndeabor, Arsenic, Cadmium and  lead