GROWTH OF Albizia lebbeck (L.) BENTHAM IN HIGHLY POLLUTED SOIL ENVIRONMENT

Abstract

The potential of Albizia lebbeck (woman‘s tongue) to reduce total petroleum hydrocarbon (TPH) content of a highly polluted soil was investigated. Unpolluted and highly polluted soils were obtained from the Oredo oil field location (Ologbo near Benin City) belonging to Nigerian Petroleum Development Company (NPDC), Benin City. Different weights of highly polluted and unpolluted soils were mixed thoroughly to obtain samples of treatments designated as 0%, 40%, 50%, 70%, 80%, and 100% polluted soil. Each soil sample weighed 2 kg. Pods of Albizia lebbeck were obtained from trees in the Senior Staff Quarters, University of Benin Campus. Plant data measured were percentage germination, plant height, number of branches, number of leaflets, fresh and dry weights. Other experimental data recorded before planting and after plant harvest were pH and EC (electrical conductivity) of soil, dominant soil microflora, TPH of soil, and aliphatic and aromatic constituents of soil samples using GC-FID. Twenty one days after planting (DAP), Albizia lebbeck seeds germinated in all treatments considered in this study. Other plant parameters evaluated showed that plants grown in 0% treatments gave the higher mean values than those grown in other treatments (40%, 50%, 70%, 80% and 100%). Generally, these values obtained for plants grown in treatments other than 0% were less than 50% of that obtained for 0% treatment. These observations showed depressive effects of crude oil pollution on plant growth. Higher values were obtained for pH and EC of soil samples after plant harvest. EC values particularly indicated improved ionic strength of soil media following plant growth and this has implication for soil-borne organisms. Dominant microflora were Pseudomonas sp. and Penicillium sp. after plant harvest. There were significant reductions in total petroleum hydrocarbon (TPH) content after plant harvest. For example, TPH values for 0% and 100% treatments before planting were 695.33 and 7073.33 mg/Kg respectively; while after plant harvest were 386.67 and 5233.33 mg/Kg. 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 plant growth. The chromatograms showed the absence of some crude oil components after plant growth, and where present but at very insignificant concentrations detected. Both aliphatic and aromatic compounds were degraded in the polluted soils. Some other studies have reported selective degradation of hydrocarbons in contaminated soil. In this study, GC-FID chromatograms showed that aliphatic hydrocarbons were degraded more than aromatics. The plant, Albizia lebbeck, has shown good ability to tolerate and sustained growth in highly polluted soil.