Volume 8, Issue 2, April Issue - 2020, Pages:176-184 |
Authors: Eze Chibuzor Nwadibe, Eze Emmanuel Aniebonam, Okobo Uchenna Jude |
Abstract: Crude oil and its derivatives are among the most potent contaminants of the environment, affecting both the biotic and abiotic components of the ecosystem. The present study was undertaken to evaluate the effects of crude oil contamination on terrestrial and aquatic microorganisms. Eight different concentrations of crude oil (Bonny light) were used to contaminate soil and water samples obtained from pristine environments. Both the control and polluted samples were organized in triplicates and the studies carried out by plate count procedures using nutrient agar and sabouraud dextrose agar for bacteria and fungi respectively. Effect of the crude oil on bacterial and fungal counts was significantly (P<0.05) inhibitory and dose-dependent with 15.0% and 20.0% levels of pollution having the highest impact on the microbial counts. In the control soil samples, bacterial numbers varied between 2.32x109 to 2.80x109 cfu/g while their numbers varied between 2.00x108 to 2.77x109 cfu/g in the test samples. For the fungi, numbers varied from 1.02x107 to 1.39x107 cfu/g in the control soil while it was reported 1.60x105 to 1.18x107 cfu/g for the test samples. Results showed that both bacteria and fungi were significantly affected by crude oil contamination, among tested microorganisms marine microorganisms demonstrated some tolerance against crude oil contamination. |
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Full Text: 1 Introduction Since the discovery of petroleum as an energy source it has remained the mainstay of many national economies. In spite of this crude oil and its products have been shown to be toxic to living organisms as well as arable lands (Eze et al. 2013; Xue et al., 2015; Wang et al., 2018; Abdullah & Peramaiyan, 2019). Oil spill incidents in Nigeria are major environmental issues especially in the oil-producing Niger Delta region. Nigeria has had over 4000 oil spills ranging from minor spills of a few hundred barrels to over half a million barrels in a single incident. Releases of petroleum into the environment occur naturally from seeps as well as from human sources. These spillages have caused much destruction of flora, fauna and arable lands in Nigerian environment (Ekpo & Udofia, 2008). On the whole, natural and human sources introduce about 380 million gallons of oil into the marine environment annually (National Research Council, 2002). About 55% from this arises from human sources via petroleum production and transportation while the remainder comes from natural seeps. Present day technology is inadequate to handle such large spills. However, techniques employed include mechanical containment with booms and removal using suction equipment and sorbents, chemical treatment with detergents, and physical removal (National Oceanic and Atmospheric Administration, 1992). Natural processes account for the removal of a large percentage of petroleum spills from the environment. Natural removal of petroleum from water takes place through evaporation, photo-oxidation, microbial degradation and utilization (Yan et al., 2018; Xingjian et al., 2018; Xinxin et al., 2019). Some microorganisms involved in crude oil degradation, detoxication and bioremediation of polluted environments. Notwithstanding, petroleum hydrocarbons have been shown to have deleterious effects on microorganisms through reduction of cell membrane permeability due to its hydrophobicity leading to reduced water and nutrient absorption (Pezeshki et al., 2000) as well as oxygen exchange between soil and the atmosphere (Adedokun & Ataga, 2007). Even though general reports abound on the negative effects of crude oil on living organisms and arable land, there is paucity of research work on its effects on microorganisms specifically. This research work was undertaken to evaluate the relative impact of crude oil on bacterial and fungal populations by checking its effects on their numbers, soil microbial respiration and phospholipids content. 2 Materials and Methods Bonny light crude oil, uncontaminated sandy loam soil, marine and freshwater samples are the materials which were used in current study. The crude oil was supplied by the Nigerian National Petroleum Corporation (NNPC), Port Harcourt, Rivers State, Nigeria. Sandy loam soil was obtained from Botany Garden, University of Nigeria. 2.1 Evaluation of the Impact of Crude Oil on Microbial Numbers in Soil Non-petroleum contaminated sandy loam soil was air dried, sieved and measured in 0.5kg portions into twenty-seven plastic buckets (13cm x 12cm). The buckets were arranged in triplicates and each triplicate set apart from the control was contaminated with one of the following concentrations of crude oil i.e. 0.5%, 1.0%, 2.0%, 2.5%, 5.0%, 10.0%, 15.0% or 20.0%v/w. After crude oil addition the soil in each bucket was thoroughly mixed. Microbiological assay was done with 1.0g of soil from each bucket every week for eight weeks. The population of viable microbial cells (bacteria and fungi) in each soil sample was determined by the spread plating technique as described by Wistreich (1997) using nutrient agar and sabouraud dextrose agar for bacterial and fungal cultivations respectively. 2.2 Evaluation of the Impact of Crude Oil on Microbial Numbers in Water Marine and freshwater samples were each measured in 200ml volumes into twenty-seven 500ml flasks grouped in triplicates. Each triplicate set excluding the controls was contaminated with one of the following concentrations of crude oil viz., 0.5%, 1.0%, 2.0%, 2.5%, 5.0%, 10.0%, 15.0% or 20.0% v/v. Uncontaminated marine and fresh water were used as control samples. Microbiological assay was carried out with 1.0ml of water from each flask every week for eight weeks. The spread plating technique was also used for the determination of microbial numbers and the media were nutrient agar and sabouraud dextrose agar for bacteria and fungi respectively. 2.3 Determination of the Effects of Crude Oil on Soil Microbial Respiration This was carried out by the method of Isermeyer (1952) which quantified the level of carbon di oxide (CO2) evolved from the soil microbes. Fifty grams of each soil sample was weighed in duplicate into beakers placed inside jars with air-tight covers. A 25 ml volume of 0.05M NaOH was introduced into each jar and the jars were instantly sealed with rubber rings. Controls for both contaminated and uncontaminated soil samples consisted of three jars, each containing 0.05M NaOH without soil. All jars were incubated at 25o C for 3 days. Following incubation, the beakers were brought out and their external surfaces washed with CO2-free water. Subsequently, 5ml of 0.5M barium chloride solution was introduced into each jar and few drops of phenolphthalein indicator were also added. This was followed by the addition of few drops of hydrochloric acid (0.05M) with continuous stirring until the colour changed from red to colourless. The rate of microbial respiration in soil was calculated with the following formula devised by Isermeyer (1952): |
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