Enzyme–based Assay for Toxicological Evaluation of Soil Ecosystem Polluted with Spent Engine Oil
O. Otitoju
Department of Biochemistry, Federal University Wukari, Nigeria
A. C. Udebuani
Department of Biotechnology, Federal University of Technology Owerri, Nigeria
M. M. Ebulue
Department of Biochemistry, University of Nigeria, Nigeria
I. N. Onwurah *
Department of Biochemistry, University of Nigeria, Nigeria
*Author to whom correspondence should be addressed.
Abstract
Aim: In this study, the experiment was designed to investigate the effect of contamination of soil ecosystem with spent engine oil at various concentrations.
Design: Soil samples were obtained from zoological garden University of Nigeria Nsukka while spent engine oil was obtained from the Mechanic Village, Nsukka. Test tubes labelled 1- 7 containing various percentages of spent engine oil 1.0, 1.5, 2.0, 2.5, 3.0, 3.5% w/w (oil-soil mixture); and into the 7th tube, the control contained only the soil sample. The study was designed for thirty-five-days (0, 14, 28 and 35 day) at various degrees of pollution by spent oil.
Results: The result showed that spent engine oil stimulated the activity of soil dehydrogenase in a concentration and time dependent manner: from (4.72 ± 0.015) mol/min at 1.0% contamination to (9.30 ± 0.021) mol/min at 3.5% contamination on day-zero; and from (5.29 ± 0.032) mol/min at 1.0% contamination to (9.78 ± 0.040) mol/min at 3.5% contamination on day-28; the activity of soil catalase was inhibited from (0.195 ± 0.005) mol/min at 1.0% contamination to (0.054 ± 0.004) mol/min at 3.5% contamination on day-zero; and from (0.18 ± 0.004) mol/min at 1.0% contamination to (0.042 ± 0.002) mol/min at 3.5% contamination on day-28. The moisture content increased from (6.4 ± 0.01) at 1.0% contamination to (24.24 ± 0.0) at 3.5% contamination on day-zero; and from (4.56 ± 0.056) at 1.0% contamination to (19.31 ± 0.0212) at 3.5% contamination on day-28. Similarly, there was an increase in total petroleum hydrocarbon (TPH) from (0.03 ± 0.0) to (0.86 ± 0.0) that cuts across days-zero to -28 at concentrations (1.0-3.5%) contamination. At increased concentrations (3.5% w/w) of contamination, hydrocarbons increased the abundance of hydrocarbon-degrading microorganisms from 3.26 x107 ± 0.02 cfu on day-zero to 6.55 x 108 ± 0.04 cfu on day-28; but on the other hand, induced a limitation on microbial diversity.
Conclusion: The concentration of the hydrocarbonclastic bacteria in the spent engine oil-contaminated soil correlated with the enzyme induction activity. These effects which altered the entire soil biochemistry could disrupt ecosystem dynamics by slowing soil organic matter mineralization and associated nutrient re-mineralization.
Keywords: Contamination, dehydrogenase, microorganisms, mineralization, hydrocarbonclastic, biodegradation