Assessment of Cu, Pb, Zn, and Cd in groundwater in areas around the derelict Enyigba Mines, south eastern Nigeria.

Abstract

The assessment of the concentration of Cu, Pb, Zn and Cd in groundwater in Enyigba is critical because of presence of numerous Pb – Zn lodes and conditions that are capable of mobilizing the metals into groundwater and pedalogical systems. Groundwater forms one of the major sources of potable water in the area. Analyses of samples of groundwater in the area however reveal that heavy metals pollution of groundwater is low. The concentration of Cu in groundwater in Enyigba vary from 0.01 – 0.07mg/l; Pb <0.001 – 0.02mg/l; Zn, 0.008 – 0.672mg/l and Cd, 0.001 – 0.02mg/l. Based on WHO Standard of 1993, these ranges of concentration of Cu and Zn in groundwater in the area are below regulation standards. The concentration of Pb in most samples is below toxic level but is however above or close to toxic level in isolated locations; Cd is above toxic level in most of the samples. Thus Pb and Cd are metals of environmental concern in the area. The concentration and standard ratio of Pb in isolated locations range from 1 to 2. Cd pollution is more widespread. The concentration and standard ratio of Cd in the area range from 1 to 10. The established pattern of distribution results from the characteristics of the ionic species generated and the properties of soil and bedrock in the area. These factors affect the metals partitioning between solid and solution phases. The implication of groundwater pollution arises partly from direct absorption of toxins through ingestion of water polluted with Cd and possibly Pb. The high Cd/Zn ratio (1 - 67) however may provide some sort of control on Cd poisoning.

KEY WORDS: heavy metals, mineralisation, Asu River Shales, concentration/standard ratio, metals speciation and ferraltic soils