Effects of Heavy Metals on Soil Enzymatic Activities in the Ishiagu Mining Area of Ebonyi State-Nigeria

Abstract

Effects of heavy metal pollution on the enzymatic activities of soils were investigated in the Ishiagu mining area of Ebonyi State, Nigeria. Soil dehydrogenase, polyphenol oxidase, hydrogen peroxidase, alkaline and acid phosphatases and urease were measured to evaluate the effects of heavy metals mining operations on soil biochemical characteristics. Results showed that the soil pH ranged from 5.04 to 6.56 while the heavy metals were of the ranges: Pb (13,754-29,491 mg/kg), Zn (1,151-2,778 mg/kg), Cd (17.65-27.71 mg/kg), Cu (9.59-39.91 mg/kg) and total heavy metals (014,932.24-32,336.62 mg/kg). Soil heavy metals concentrations significantly decreased with the increase of distance from the mining pit while soil pH increased with the increase of the distance from the mining pit. Analysis of the soil enzyme activities indicated a significant positive correlation at P≤ 0.05 between soil enzyme activities and soil pH. On the contrary, the activities of dehydrogenase, polyphenol oxidase, hydrogen peroxidase, alkaline and acid phosphatases and urease showed significant negative correlation at P≤ 0.05 with the heavy metal contents except for Zn against dehydrogenase activity and Cd against hydrogen preoxidase and urase activities that were though negative but statistically not significantly correlated at P≤ 0.05. This showed that the activities of the enzymes analysed could be used as sensitive indicators of heavy metals contamination. The results in general indicated that the mining operations at Ishiagu, Ebonyi State affect the soil quality due to heavy metal contamination.