ABSTRACT
Aims: To remove hydrocarbons from crude oil polluted agricultural soil using two selected plant species.Study Design:Mature seeds of Schwenkia americanaL. and Spermacoce ocymoidesBurm. f. were propagated onto a sterile unpolluted agricultural soil. Seedlings were transplanted into an 8 kg potted homogenised polluted soil for remediation. Place and Duration of Study:Polluted agricultural soil collected from Ogoniland, Rivers State, Nigeria, Ecological Centre of the University of Port Harcourt Nigeria, between May 2017 and February 2018.Methodology:Standard methods were employed for laboratory analyses. Reagents used were of analytical grades with high purity. Results:Twelves weeks after planting (WAP), total petroleum hydrocarbons (TPH) decreased from 17962.11±1000.00 mg/kg to 117.64±30.27 and 117.45±14.76 mg/kg in S. americanaand for S. ocymoidesremediated groups respectively, while polycyclic aromatic hydrocarbons (PAH) decreased from 440.97±1.00 mg/kg to 120.99±50.05, and 181.97±158.69 mg/kg for S. americanaand for S. ocymoidesremediated groups respectively. While oil content decreased to 1.02±0.09 and 1.15±0.21 ppm for S. americanaand S. ocymoidesremediated groups respectively from an initial 3.19±0.10 ppm recorded at the onset of remediation, organic carbon decreased from 2.78±0.01% to 2.16±0.06 and 2.07±0.18% for S. americanaand S. ocymoidesremediated groups respectively. With regards to TPH, the percentage recovery moved towards normal values (510.27 and 509.02%), however, with regards PAH, the values nosedived indicating a failure in restoration. By 4, 8 and 12 WAP, the treatment restored the values towards normal values (1.08, 7.30, 10.58,10.81 and 14.05%), however, the treatment using S. ocymoides, by 12 WAP, plunged, indicating failure to restore the polluted soil, especially with regards to the oil content, while by 8 and 12 WAP, the treatments restored the polluted soil towards normal values (3.33, 11.11 and 13.33), with regards to the organic carbon.Conclusion:The quality of the crude oil polluted agricultural soil was enhanced through phytoremediation with these plant species. This contention is supported by the diminution of hydrocarbons, organic carbon and the oil content of the remediated groups after the 12 weeks remediation
ABSTRACT
Aims: To investigate the variation in the activities of some soil enzymes and microbial respiration during phytoremediation of crude oil polluted agricultural soil. Study Design: Indigenous plants of a crude oil polluted agricultural farmland were harvested and identified. Two species (Schwenkia americana L. and Spermacoce ocymoides Burm. f.) were selected for this study. Nursery was set up using sterile soil and mature and viable seeds of selected species, and germinated seedlings were transplanted into an 8 kg potted homogenised polluted soil for remediation. Place and Duration of Study: Polluted agricultural soil from Ogoniland Nigeria, University of Port Harcourt ecological garden, between May 2017 and February 2018. Methodology: Protease activity was determined based on the amino acids released after incubation of soil with sodium caseinate. Phosphatase activities determination was based on determining the degradation extent of ρ-nitrophenol phosphate (PNPP) by the samples. Dehydrogenase activity was determined based on estimation of 2,3,5- triphenyltetrazolium chloride (TTC) reduction to triphenyl formazan (TPF) in soils after incubation. The substrate induced method was adapted to estimate the respiratory activity. Organic matter was determined by weight loss on ignition method. Results: Dehydrogenase activities in remediated groups increased after 4 weeks but decreased at the end of the remediation period. Protease and phosphatase activities, and soil organic matter of remediated groups reduced over time while the soil microbial respiratory activity reduced at the end of 12 weeks remediation. There was a restoration of the polluted soils by the treatments towards normalcy with regards to activities of proteases, acid and alkaline phosphatases, and dehydrogenases. Conclusion: Soil microbial activities can reflect soil quality, and soil enzyme activities can directly reflect the metabolic need and nutrient availability of soil microorganisms. The extracellular enzymes (protease, dehydrogenase, acid and alkaline phosphatase) were shown to vary with crude oil pollution relative to time thus indicating ameliorative effects.