Ecological risk assessment and phytoremediation of spent engine oil contaminated soils of selected mechanic workshops in Imo State
Date
2023-05
Authors
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Publisher
Federal University of Technology, Owerri
Abstract
Assessment of the ecotoxicological risk of indiscriminate disposal of spent engine oil on terrestrial ecosystem was investigated using physicochemical, biochemical, and bioterance
assays. Soil samples were collected from a depth of 0-20cm and analyzed using standard analytical protocols. Acute toxicity tests were conducted based on germination and seedling
establishment of higher plants (Zea mays, G. maxV. unguiculata), Earthworms (mortality rate) and microorganisms (inhibitory effects) which covered a wide range of short-term lethal and sub-lethal endpoints used for risk characterization and analyzed using Probit analysis. Results obtained showed that majority of the mechanics who are within 20-30 age bracket were found in Owerri (22.42%) while the least was found in Okigwe (12.98%); on weekly basis, 42 vehicles are serviced in Owerri; 27 inOrlu while 21 is been serviced in Okigwe respectively. Total annual volume of spent engine oil generated (in litres) was highest in Owerri zone (124,489.36L) while the least value was obtained in Orlu zone (18,434.52L). A significant volume 168 (49.56%) of the spent engine oil is been disposed into the immediate environment with others being sold off 41 (12.09%); given out for free 66 (19.47%); and taken by car owners 64 (18.88%). Axonopuss compressus, Aspillia africana, and Chromolaena odorata species were the dominant plant species identified in the order: Axonopuss compressus>Aspillia africana> Chromolaena odorata. Mean values of physical and chemical properties of soil indicated alteration of parameters analyzed relative to the control. The mean concentrations of heavy metals across the zones ranged from Pb(1.045 ± 0.1 to 1.534 ± 0.2), As (1.761 ± 0.3 to 1.805 ± 0.3), Cr (0.272 ± 0.01 to 0.273 ± 0.01), Cd (0.302 ± 0.02 to 0.606 ± 0.03), Ni (0.918 ± 0.03 to 0.932 ± 0.03), Co (1.278 ± 0.1 to 1.324 ± 0.2), Fe (63.927 ± 3.34 to 69.563 ± 3.53), Cu (12.446 ± 2.14 to 12.964 ± 2.42), Zn (156.121 ± 28.01 to 156.137 ± 28.12), and Al (1.353 ± 0.2 to 1.353 ± 0.12) mg/kg with a distribution pattern of Zn>Fe>Cu>As>Al>Co>Pb>Ni>Cd>Cr. Concentration of heavy metals were significantly (p<0.05) higher at the polluted sites than the control and above WHO permissible limits. Mean concentration of PAHs ranged between Owerri zone (0.03 ± 0.01 to 1.980 ± 0.36mg/kg) Orlu zone (0.004 ± 0.001 to 1.614 ± 0.10 mg/kg), and in Okigwe zone (0.01 ±0.001 to 1.418 ± 0.19mg/kg) with distribution pattern of Nap>Pyr>Mepl>Ind>Acpt>Flu>Bbf>B(ghi)p>B(g)p>Bkf>Da>An>Acph across the zones.Maximum Concentration of TPH
was recorded in Owerriwhile the minimum value was gotten from the control site. Mean values of TPH were in the order: Owerri>Orlu>Okigwe>control. Result of acute toxicity assay showed that Zea mays exhibited more sensitivity than V. unguiculata and G. max. The microbial absorbance rate depended on the dose and type of organism in the order of:
Acinetobacter>Enterobacter> Bacillus species >Pseudomonas. Mortality in earthworm was noted as concentration increased. Values of Risk Quotient for Zea mays, V. unguiculata, G. max and earthworm ranged from low risk to very high risk based on the estimated PNEC values. The microorganisms differed slightly in biotolerance to spent engine oil exposure based on estimated risk quotients. Exposure to spent engine oil posed minimal risk to Pseudomonas sp., Bacillus sp., and Acinetobacter sp., at the estimated PNECs with values less than unity (<1). Risk quotient values for Enterobacter sp. indicated a high risk with values above unity. Variable xxi concentrations of heavy metals were accumulated by the plants from soil and were stored in the root, shoot and leaf except for A. compressus that accumulated values less than one (<1) for Pb and As. Metal accumulation pattern were in the order C. odorat>A.africana>A.compressus. C. odorata and A. africana exhibited characteristics typical of a phytoextractor while A. compressus could be applied as a phytostabiliser of spent engine oil polluted soils. The sensitivities exhibited by the organisms exposed to spent engine oil indicate the possibility of using them as bioindicators and for assessing the efficacy of phytoremediation process. Spent engine oil adversely affected the organisms in each scenario in a dose dependent manner. Overall, these findings proved that spent engine oil greatly altered soil properties and also repressed the growth of organisms in the ecosystem thereby strengthening the need to curb indiscriminate disposal of spent oil on the environment by mechanics in the business of auto repairs to forestall possible pollution problems of other components of the food chain.
Description
The thesis is for the award of Doctor of Philosophy ( Ph.D) in Biology (Environmental Conservation and Management)
Keywords
Spent engine oil, indigenous plants, ecosystem, risk ssessment, phytoremediation, bioassays, zea mays, G. max, V. unguiculata, earthworm, risk quotient., Department of Biology
Citation
Azorji, J. N. (2023 ). Ecological risk assessment and phytoremediation of spent engine oil contaminated soils of selected mechanic workshops in Imo State (Unpublished Doctoral Thesis). Federal University of Technology, Owerri, Nigeria