Impact of Solid Waste Disposal on Soil Physicochemical Parameters and Selected Enzyme Activities: A Case Study from Nekede Dumpsite, Nigeria

Abstract

This study assessed the influence of solid waste disposal on soil physicochemical parameters in Nekede dumpsite Owerri, Imo state Nigeria. The study area is a solid waste dumpsite located between latitude 5° 25' 59.99"N and longitude 7°01'60.00"E DMS coordinates along No. 1 old Nekede road and beside the Otamiri river. The study area was partitioned into four (4) quadrants while facing the river with samples collected at three (3) different depths of 0-5cm, 5-10cm, and 10-15cm per quadrant. From each quadrant, samples were collected at twenty different points and homogenized for each of the depths, summing up three samples for each quadrant. The control samples were collected 500m away from the dumpsite, devoid of any form of waste dumping. Selected soil enzyme activities and heavy metals in samples were determined using standard biochemical procedures. Heavy metals examined include copper (Cu), zinc (Zn), iron (Fe), nickel (Ni), cadmium (Cd), lead (Pb), mercury (Hg), and chromium (Cr). From our findings, soil dehydrogenase, hydrogen peroxidase, acid, and alkaline phosphatases were examined. Soil temperature, moisture, pH, exchangeable acidity, organic carbon and cation exchange capacity varied between 27.33±0.03 °C to 28.70±0.01 °C, 0.80±0.03 % to 13.00±0.01 %, 7.36±0.03 to 8.61±0.01, 0.20±0.01 mEq/10g soil to 1.00meq/10g soil, 0.32±0.02 % to 1.32±0.03 % and 7.91±0.01 to 12.58±0.01 cmol/kg respectively. All heavy metals investigated in this dumpsite varied from highest to lowest in concentration in the following order Pb>Fe>Zn>Cd>Cu>Cr>Hg>Ni with concentration of heavy metals in vegetables from the study area abundant in Cu, Fe, Ni and Cr. Absence of Cd, Hg and Pb were recorded in all vegetables. Values recorded for soil dehydrogenase, hydrogen peroxidase, acid and alkaline phosphatase enzymes varied between 6.85±0.01 % to 12.79±0.01 %, 0.20±0.01 (0.1/ml KMnO4/g) to 3.40±0.01 (0.1/ml KMnO4/g), 1.72±0.05 (mg p-nitrophenyl/g/6hrs) to 3.95±0.01 (mg p-nitrophenyl/g/6hrs) and 4.72 ± 0.03 (mg p-nitrophenyl/g/hr) to 7.20 ± 0.04 (mg p-nitrophenyl/g/6hrs) respectively. For majority of the parameters measured, values recorded were within the permissible limit for a healthy soil. However, vegetables from the dumpsite assimilated nickel (Ni) more than other heavy metals studied, thus showing their possible bioremediation potential in an environment polluted with nickel.