ASSESSING SUCCESSIVE PLANT GROWTH ON PETROLEUM HYDROCARBON DEGRADATION IN HIGHLY POLLUTED SOIL AUGMENTED WITH WOOD ASH
D. E. VWIOKO, C.E. OMAMOGHO

Abstract
Successive growth of Corchorus aestuans L. and Lagenaria siceraria (Mol.) Standl. in crude oil polluted soil supplemented with wood ash were evaluated for degradation and compositional changes of crude oil components in soil for 5.5 months. The vegetative parameters recorded were germination, plant height or vine length and leaf elongation rate. Total petroleum of hydrocarbon (TPH) and pH of the soil samples (unpolluted and polluted) obtained from the field were determined before the commencement of study. GC – FID analyses of differently prepared soil samples obtained at the end of the experiments were carried out as well. Mean values obtained for TPH and pH of unpolluted and polluted soil from the field were 10.90 ppm and 40,173.90 ppm, 6.26 and 4.67, respectively. The application of wood ash as soil supplements in crude oil polluted soil changed the hydrophobic soil condition to hydrophilic. This also improves the pH toward neutral. Germination was observed in all concentrations of soil tested. Percent germination of C. aestuans was 40% and below while L. siceraria was higher. Over 90% of C. aestuans seedlings could not survive up to 60 days in polluted soil. Growth inhibition in polluted soil was recorded. The growth of L. siceraria plants on the same soil was also inhibited but they sustained growth for a longer period. Minimal plant growth enhancement was observed for plants grown in 50% polluted soil supplemented with 20g wood ash. The GC-FID chromatograms showed presence of aliphatic and aromatic hydrocarbons at high concentration in polluted soil obtained from the field. These petroleum hydrocarbon compounds were degraded in soil following wood ash supplementation and plant growth. The chromatograms showed the absence of some crude oil components after plant growth, and where present but at very insignificant concentrations detected. Interestingly, both aliphatic and aromatic compounds were degraded following the wood ash supplementation in polluted soil. In contrast, some other studies have reported selective degradation of hydrocarbons in contaminated soil. The challenge in applying accelerated biodegradation techniques is not the ability to stimulate bacteria to degrade hydrocarbons; it is judging how low the hydrocarbon concentration can be.

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