Removal of Nigerian light crude oil in soil over a 12-month period

A study was carried out to aid in understanding the effect of various concentrations (10, 20, 30, 40% v/w) of Nigerian light crude oil (Transniger pipeline crude, TNP) deliberately spilled on soil will have on the indigenous bacterial population and the role of the bacteria in the removal of the oil. The average total counts of aerobic heterotrophs and crude oil utilizing bacteria in oil-impacted soils were 10 8 and 10 6 CFU/g , respectively, while in the untreated soil the total counts of the two groups of bacteria were low. The counts of the two groups of bacteria decreased with increasing oil concentration in the soil. Significantly higher numbers of total aerobic heterotrophs were recorded between May and July while those of crude oil utilizing bacteria were recorded between February and April probably due to differences in metabolic rates of the organisms as influenced by environmental conditions. The crude oil utilizing bacteria were identified as species of Bacillus, Pseudomonas, Vibrio, Micrococcus and Alcaligenes. The total extent of crude oil degradation by these organisms ranged from 26.7% to 43.3% after 16 days. GC analysis of the crude oil extracted from soil showed that hydrocarbon components C 14 to C 32 were extensively lowered in soil polluted with 10% and 20% (v/w) crude oil after 12 months but moderately lowered in soil treated with 30% (v/w) crude oil over the same period. In soil contaminated with 40% (v/w) of the same crude oil, minimal degradation of C 14 to C 32 was observed. The results indicate that the quantity of crude oil spilled in soil and the age of the contamination influence the rate and total extent of disappearance of the oil in the environment.