The Environmentalist, 23, 249–254, 2003  2004 Kluwer Academic Publishers. Manufactured in The Netherlands. Stimulated Biodegradation of Crude Oil in Soil Amended with Periwinkle Shells U.J.J. IJAH ∗ and M. NDANA ∗∗ Department of Biological Sciences, Federal University of Technology, P.M.B 65, Minna, Nigeria Summary. The potential of periwinkle shell (PS) in enhancing the microbial break down of crude oil spilled in soil were studied. The results revealed that the counts of crude oil degrading bacteria in oil-polluted soil fortified with PS were higher than the counts in unfortified soil. The rates and total extent of crude oil biodegradation in the soil were stimulated by the amendment. About 43.4 percent of crude oil was degraded in unfortified soil after 16 days as compared to 70.1 percent oil biodegradation, which occurred in PS fortified soil during the same period. These values were significantly (P< 0.05) different from each other. Amendment of the soil with PS also raised the pH of the soil from acidic to alkaline range. The crude oil degrading microorganisms identified in PS amended soil were of the genus Pseudomonas, Bacillus, Micrococcus, Acinetobacter, Penicillium, Aspergillus, Mucor and Rhizopus. Similarly, Pseudomonas, Bacillus, Micrococcus, Mucor, Aspergillus and Penicillium were identified as crude oil degrading microorganisms in unamended soil. The bacteria formed either stable or unstable emulsions, suggesting that the organisms produce surface-active agents (biosurfactants) during the biodegradation process. The results of this study indicate that PS can be used in reclaiming oil-polluted soil. Keywords: stimulated biodegradation, crude oil, periwinkle shell, soil Introduction In recent times, various approaches have been adopted in reclaiming oil-spilled soils. These include the use of oil degrading microorganisms (microbial seeding), inorganic fertilizer, chicken droppings, cow dung, lim- ing and tilling (Leahy and Colwell, 1990; Miller and Donahue, 1990; Ijah and George, 1998; Ijah and Ken- neth, 2002; Ijah and Antai, 2003). Inorganic fertilizer and chicken droppings provide nitrogen and phospho- rus to oil degrading microorganisms. Chicken drop- pings also harbour crude oil degrading microorgan- isms. Ijah and Antai (2003) reported that 68.2 percent crude oil was mineralized in soil fortified with chicken ∗ Dr. Udeme J.J. Ijah, the author for correspondence purposes (e-mail: dr_ijah@yahoo.co.uk), is the Head of the Microbiology Unit in the Department of Biological Sciences, at the Federal Uni- versity of Technology. ∗∗ M. Ndana is based in the School of Midwifery, Minna, Nigeria. droppings as compared to 50.7 percent oil mineraliza- tion in unfortified soil. It has also been reported that 87.5 percent crude oil was degraded in soil fortified with NPK fertilizer while 75 percent of the same oil was degraded in soil fortified with chicken droppings after 10 weeks (Ijah and Safiyanu, 2003). In unfortified oil polluted soil 56.3 percent crude oil degradation was recorded over the same period. Similarly, counts of crude oil uti- lizing bacteria were higher in fortified soil than un- fortified soil. We also found in a laboratory exper- iment that 70 percent of crude oil was degraded in soil amended with cow dung as compared to 35 per- cent crude oil degradation in unamended soil (Ijah and Kenneth, 2002). In addition the population of crude oil degrading bacteria in the soil amended with cow dung was higher than that of the unamended oil pol- luted soil. The aim of the present study was to evaluate the potential of periwinkle shells in enhancing crude oil