Journal of Applied Microbiology ISSN 1364-5072 REVIEW ARTICLE Microbe-aliphatic hydrocarbon interactions in soil: implications for biodegradation and bioremediation J.L. Stroud1, G.I. Paton2,3 and K.T. Semple1 1 Department of Environmental Science, Faculty of Science and Technology, Lancaster University, Lancaster, UK 2 School of Biological Sciences, University of Aberdeen, Aberdeen, UK 3 Remedios Ltd, Aberdeen Science and Technology Park, Aberdeen, UK Keywords bioaccessibility, bioavailability, biodegradation, contaminated land, organic contaminants. Correspondence K.T. Semple, Department of Environmental Science, Faculty of Science and Technology, Lancaster University, Lancaster, LA1 4YQ, UK. E-mail: k.semple@lancaster.ac.uk 2006 ⁄ 1369: received 29 September 2006, revised 14 March 2007 and accepted 20 March 2007 doi:10.1111/j.1365-2672.2007.03401.x Summary Aliphatic hydrocarbons make up a substantial portion of organic contamination in the terrestrial environment. However, most studies have focussed on the fate and behaviour of aromatic contaminants in soil. Despite structural differences between aromatic and aliphatic hydrocarbons, both classes of contaminants are subject to physicochemical processes, which can affect the degree of loss, sequestration and interaction with soil microflora. Given the nature of hydrocarbon contamination of soils and the importance of bioremediation strategies, understanding the fate and behaviour of aliphatic hydrocarbons is imperative, particularly microbe–contaminant interactions. Biodegradation by microbes is the key removal process of hydrocarbons in soils, which is controlled by hydrocarbon physicochemistry, environmental conditions, bioavailability and the presence of catabolically active microbes. Therefore, the aims of this review are (i) to consider the physicochemical properties of aliphatic hydrocarbons and highlight mechanisms controlling their fate and behaviour in soil; (ii) to discuss the bioavailability and bioaccessibility of aliphatic hydrocarbons in soil, with particular attention being paid to biodegradation, and (iii) to briefly consider bioremediation techniques that may be applied to remove aliphatic hydrocarbons from soil. Introduction Hydrocarbons in the environment Hydrocarbon pollution is ubiquitous in the environment and accounts for over 15% of all pollution incidents in England and Wales (Environment Agency 2006). Oil contamination is reported to be a common pollution incident with almost nine incidents per day in 2005 (Environment Agency 2006). Details of actual contamination of the terrestrial environment by oil are difficult to quantify because of the unintentional nature of contamination (largely through accidental spillage). However, it is estimated that over one million tonnes of oil are spilled into UK terrestrial ecosystems every year (Ripley et al. 2002). This is a significant problem receiving considerable political and scientific interest, and the Environment Agency of England and Wales had recently published a report investigating the risk from petroleum hydrocarbons in soils (Askari and Pollard 2005). Contaminated land is costly to clean up; for example, in the USA, the cost is expected to exceed US $1 trillion (Maier et al. 2000), where 90% of the sites undergoing remediation are linked to petroleum hydrocarbons (Cole 1994). Bioremediation is a cost-effective strategy, and it is reported that approximately 25% of all petroleum-contaminated land is being cleaned up using natural attenuation strategies (Holden et al. 2002). Thus, in order to predict how successful bioremediation will be, research into the fate and behaviour of hydrocarbons in soil is important. To date, research has centered on aromatic contaminants, particularly polycyclic aromatic hydrocarbons (PAHs), as these contaminants are the current risk drivers for land remediation (Askari and Pollard 2005). However, ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 1239 J.L. Stroud et al. aliphatic hydrocarbons are significant contaminants; oil pollution in the UK is dominated by diesel, with petrol and diesel containing up to 90% of aliphatic hydrocarbons by volume dominated by C14-C20 alkanes. However, despite aromatic contaminants receiving the greatest research attention, this class of chemical only equates to less than 5% by volume (Block et al. 1991). their fate and behaviour in soil; (ii) to discuss the bioavailability and bioaccessibility of aliphatic hydrocarbons in soil, with particular attention being paid to biodegradation, and (iii) to briefly consider bioremediation techniques that may be applied to remove aliphatic hydrocarbons from soil. Aliphatic hydrocarbons in soil Aims Given the nature of hydrocarbon contamination of soils and the importance of bioremediation strategies, understanding the fate and behaviour of aliphatic hydrocarbons is imperative, particularly microbe–contaminant interactions. Biodegradation by microbes is the key removal process of hydrocarbons in soils, which is controlled by hydrocarbon physicochemistry, environmental conditions, bioavailability and the presence of catabolically active microbes. Therefore, the aims of this review are (i) to consider the physicochemical properties of aliphatic hydrocarbons and highlight the mechanisms controlling Physicochemical properties of aliphatic hydrocarbons Aliphatic hydrocarbons are defined as open-chain methane derivatives, which are both non-aromatic and non-cyclic organic compounds, containing carbon and hydrogen. Aliphatic hydrocarbons can be subdivided into three structurally different groups: (i) alkanes – saturated hydrocarbons with single C-C bonds; (ii) alkenes – unsaturated hydrocarbons containing double C=C bonding; and (iii) alkynes – unsaturated hydrocarbons containing a triple C ” C bond. Table 1 shows the members of the aliphatic groups and their properties. Table 1 Physicochemical properties of selected hydrocarbons (Verschueren 1983; Howard and Meyln 1997) Hydrocarbon group Name Formula Molecular weight (g mol)1) Aliphatic Alkane Tetradecane C14H30 198Æ38 5Æ5 253 0Æ000 282 7Æ2 MODEL Alkane Hexadecane C16H34 226Æ44 18 287 0Æ0009 9Æ1 Alkene Hexadecene C16H32 224Æ43 3–5 274 N⁄A N⁄A Alkyne Hexadecyne C16H30 222Æ42 15 148 N⁄A N⁄A PAH Naphthalene C10H8 128Æ18 79–83 217Æ9 30 3Æ36 MODEL PAH Phenanthrene C14H10 178Æ22 97–101 340 1Æ1 4Æ16 PAH Pyrene C16H10 202Æ6 156 404 0Æ135 5Æ19 PAH Benzo[a]Pyrene C20H12 252Æ31 175–179 495 0Æ0038 6Æ06 Aromatic Structure Melting point (C) Boiling point (C) Solubility (mg l)1) log Kow N ⁄ A, Data not available. 1240 ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Bioavailability of hydrocarbons in soil Mid-length (C14-C20) alkanes are non-polar, virtually water insoluble hydrocarbons with increasing melting and boiling points as carbon number increases within the molecule. Typically, these alkanes have low aqueous solubilities; for example, hexadecane has a water solubility of 0Æ9 lg l)1 and is in a liquid state at room temperature. Collectively, these physicochemical properties mean that mid-length aliphatic contaminants are not readily volatilized or leached from soil. Despite this, hydrocarbons may be subjected to a number of physical, chemical and biological processes in soil, with microbial degradation representing the major loss process. Further, it is well established that interactions between hydrophobic organic contaminants (HOCs), of which most studies have focussed on aromatic hydrocarbons, may also be important in controlling the fate and behaviour in soil, involving interactions with the mineral and organic fractions, which may result in a reduction in biological and chemical availability and allowing these contaminants to persist in soil. A comparison between the properties of aliphatic and aromatic hydrocarbons is shown on Table 1. Hexadecane is a very hydrophobic hydrocarbon, being three orders of magnitude more insoluble and having a higher octanol-water partition coefficient than phenanthrene. Further, hydrophobicity has been determined to be a crucial property in controlling the organic contaminant behaviour in soil, affecting sequestration and both chemical and biological availability (Reid et al. 2000a). Due to the limited research on aliphatic sequestration and bioavailability, their behaviour is discussed in relation to PAHs in this review, where appropriate. Bioavailability of hydrocarbons in soil as key components with sorption described as reversible (Pan et al. 2006), and (ii) hard carbon (glassy) defined as rigid, condensed structures with humin (Pan et al. 2006), kerogen (Cornelissen et al. 2005) and pyrogenic carbons (Cornelissen et al. 2005) as commonly identified components. Sorption of hydrocarbons within the glassy region is characterized by irreversible sequestration (Xing and Pignatello 1996). The extent to which a chemical partitions into the organic matter is described by Koc, but may also be described by Kow (Table 1); aliphatic hydrocarbons can strongly partition into organic matter and diffuse into the three-dimensional structure of the organic matter. Hydrocarbons may be sequestered within the soil through sorption to organic matter and mineral fractions and ⁄ or diffuse into the three-dimensional structure of the soil (Fig. 1); the degree to which these physical interactions occur increases with time, and has been termed ‘ageing’ (Hatzinger and Alexander 2005). It has been well documented that as soil–contaminant contact time increases, there are commensurate decreases in mild chemical extraction and biodegradation (Semple et al. 2003). Interactions between soil components and chemical availability and biological interactions have mainly focussed on aromatic hydrocarbons, and have only been reported for aliphatic hydrocarbons in a few studies. For example, Noordman et al. (2002) reported that mass transport limitations were important after investigating the biodegradation of hexadecane in a variety of matrix sizes. The smaller the pore size, the lower the extent of mineralization; the smallest pore size of 6 nm (Silica 60) led to the lowest extent of degradation. Interactions between soil and aliphatic hydrocarbons Before considering the interactions between soil microorganisms and aliphatic hydrocarbons, putative interactions between soil and these organic contaminants must be briefly considered, as it is well known that soil–contaminant interactions can affect microbial degradation. Soil is composed of inorganic and organic components separated by pores containing air or water. The interactions between hydrocarbons and mineral surfaces (clay, silt and sand) are only significant when the organic matter content is <0Æ1% (Schwarzenbach and Westall 1981). Thus, organic matter is very important in the fate and behaviour of organic contaminants, including aliphatic hydrocarbons, in soil. Such mechanisms of interaction between organic matter and organic contaminants are not the major focus of this review and have been reviewed elsewhere (Pignatello and Xing 1996; Cornelissen et al. 1998). In summary, organic matter can be divided into two distinct phases: (i) soft carbon (rubbery) is defined as expanded, flexible structures with humic and fulvic acids Interactions between microflora and hydrocarbons in soil Bioavailability and bioaccessibility – definition and measurement Understanding the term ‘bioavailability’ is complicated because of a number of interpretations in published literature. In an attempt to clarify this matter, Semple et al. (2004) proposed two linked definitions, bioavailability and bioaccessibility. A bioavailable compound is defined as ‘a compound which is freely available to cross an organism’s membrane from the medium the organism inhabits at a given point in time’. A bioaccessible compound is described as ‘a compound which is available to cross an organisms’ membrane from the environment it inhabits, if the organism has access to it; however, it may either be physically removed from the organism, or only bioavailable after a period of time’ (Semple et al. 2004). In considering the methods used ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 1241 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License J.L. Stroud et al. J.L. Stroud et al. NAPL fraction Surface sorption Water soluble fraction Diffusion into glassy organic matter Mineral fraction Surface sorption Microbes Diffusion into pores Diffusion into rubbery organic matter Figure 1 Possible interactions between soil matrices and aliphatic hydrocarbons. to determine microbial degradation as well as the use of chemical extractions to predict microbial degradation in published literature, it is reasonable to presume that the latter definition (bioaccessibility) is more likely to be measured both biologically and chemically. For the purposes of this review, bioaccessibility will relate to microbial degradation. Measuring bioaccessibility is difficult, as this will be controlled by the nature of interaction between the organism and the chemical, and the physical location of the chemical in relation to the organism and likelihood of desorption from soil particles with time (Semple et al. 2003, 2004). Further, the methods used to chemically or biologically determine microbe–contaminant interactions will also constrain the measurements. By way of explanation, Reid et al. (2000a) and Stokes et al. (2005) comprehensively reviewed the methods for assessing bioavailability with biological and chemical techniques. The reviews highlighted that biodegradation assays rely on soil slurries and solubilization target contaminants, which gives an estimation of bioaccessibility rather than bioavailability. For example, 14C-hydrocarbon respirometry (Reid et al. 2001) involved mixing soil with liquid media, forming a slurry. Recently, it has been shown that this puts considerable bias towards a more planktonic aqueous phase biodegradation, reducing sorbed phase biodegradation (Woo et al. 2004). 1242 The chemical determination of bioaccessibility has attracted considerable attention, with comparisons between microbial degradation assays and various chemical extractions being the most widely investigated (Semple et al. 2003; Stokes et al. 2005). In comparison to microbial degradation, mild organic solvent extractions have been reported extensively, with some success (Kelsey et al. 1997; Liste and Alexander 2002), whereas other authors have reported no correlation (Macleod and Semple 2000; Macleod and Semple 2003). More promisingly, Tenax, XAD-4 and cyclodextrin extractions have been more successful as they rely on desorbing fractions of HOCs, with good correlations with microbial degradation mainly for aromatic hydrocarbons (Cornelissen et al. 1997; Reid et al. 2000b; Dew et al. 2005; Stokes et al. 2005; Doick et al. 2006) However, only a few studies have investigated this for aliphatic hydrocarbons, showing that the desorbed fraction is less than that of the microbially degraded fraction, indicating that contaminants can be degraded without prior desorption to the aqueous phase (Huesemann et al. 2003, 2004). Thus, can bioaccessibility be adequately measured for aliphatic hydrocarbons using these extraction techniques described for aromatic hydrocarbons? To some extent, the use of biomarkers in the field of environmental forensics has enabled a thorough technique to connect genuine environmental behaviour (sequestra- ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Bioavailability of hydrocarbons in soil tion, degradation and ageing) to bioavailability. For example, Wang et al. (2006) reviewed this area extensively and related the nature of refined and crude oils to certain biomarker chemicals. For example, terpanes and steranes (multi-ringed cycloalkanes found in crude oils) of varying sizes are widely used because of their recalcitrant nature, and their concentration can be used to identify both the source of the hydrocarbon pollution and the relative time since release. The application of this approach is widely acknowledged for crude oils. Such petroleum biomarkers are widely used in the investigation of hydrocarbon spills (Page et al. 1988; Barakat et al. 1999; Zakaria et al. 2001). However, most of these examples are concerned with marine incidents with none reported in the terrestrial environment. These data enabled the users to establish the actual origin of the material and the likely discharge volume that had occurred. Refined petroleum fuels are obtained from crude oil through refining processes, and thus the chemical composition of this feedstock, the refinery techniques and conditions and the intended products determine the relationship between the crude and the refined material. In the case of lubrication oils, Speight (1999) points out that biomarkers are located in the high carbon number end and these products have more markers than most crude oils and petroleum products. In oils and petroleum products, aromatic steranes are additional useful compounds for biomarking on account of their resistance to biodegradation. Biodegradation of hydrocarbons in soil The initial step in the aerobic degradation of saturated, aliphatic (n-alkanes) compounds involves the oxygenase enzyme ‘attacking’ the terminal methyl group where a primary alcohol is formed (Sepic et al. 1995; Koma et al. 2001; van Hamme et al. 2003). The alcohol is further oxidized to the corresponding aldehyde and fatty acid. The fatty acid is oxidized by cytoplasmic b-oxidation enzymes to tricarboxylic acid (TCA) (van Hamme et al. 2003). Studies on the oxidation of alkenes have been limited to the degradation of terminal alkenes (1-alkenes) with little attention to the internal alkene oxidation (Morgan and Watkinson 1994). The double bond position is a factor affecting alkene degradability as 1-alkenes are more easily degradable than alkenes with an internal double bond. Based upon the initial attack of aerobic oxidation, which can occur at either the double bond or the saturated chain end (i.e. methyl group), four main products can be recognized. The oxidation of the methyl group can form either (i) alkenol or fatty acids or (ii) primary or secondary alcohols or methyl ketones, whereas the oxidation of the double bond produces either (i) an epoxide or (ii) a diol (Britton 1984; Morgan and Watkinson 1994). Bioavailability of hydrocarbons in soil Although a number of studies (e.g., Chayabutra and Ju 2000; Grishchenkov et al. 2000; van Hamme et al. 2003) have illustrated that n-alkanes and branched alkanes can be degraded under anaerobic conditions, the anaerobic pathway of aliphatic hydrocarbon metabolism has not been described in great detail. A number of studies have suggested that the degradation of n-hexane can be used as a model for the degradation pathway of n-alkanes by a range of anaerobic micro-organisms (Heider et al. 1999; Widdel and Rabus 2001; Wilkes et al. 2003). The initial step of this pathway is by the activation of n-alkane at C2 with fumarate to form (1-methylalkyl) succinate, which is further activated by HSCoA (coenzyme A, CoA) to yield (1-methylalkyl) succinyl-CoA (Heider et al. 1999; Wilkes et al. 2003). The latter compound goes though carbon skeleton rearrangement to form (2-methylalkyl) malonylCoA, which is then decarboxylated to 4-methylalkanoylCoA and then oxidized by b-oxidation to produce CO2 as the end product (Wilkes et al. 2003). The biodegradable fraction of organic contaminants in soil is defined throughout the literature as the fraction that may be easily desorbed to or is desorbed from soil and present in the aqueous phase (Alexander 2000; Reid et al. 2000a; Semple et al. 2003). Whilst older microbiological studies show that microbes are only able to utilize dissolved HOCs (Wodzinski and Coyle 1974; Ogram et al. 1985), those studies had limitations as it is now known that common bacterial culturing techniques may have led to the isolation of degraders that cannot utilize hydrocarbons sorbed to soil. Micro-organisms capable of sorbed-hydrocarbon biodegradation require a sorbed form of growth substrate (Tang et al. 1998). Thus, more recent studies comparing the biodegradation of organic contaminants, which are present as dissolved or sorbed substrates, have shown that sorption is not limiting to the biodegradation of either aromatic (Laor et al. 1996) or aliphatic hydrocarbons (Holden et al. 2002). Indeed, Pignatello et al. (1983) hypothesized that the biodegradation of HOCs occurs at the soil surface rather in the aqueous phase. Additionally, much our understanding of this phenomenon comes from the measured response of the relatively water-soluble herbicides such as 2,4-dichlorophenolxyacetic acid (2, 4-D) (Ogram et al. 1985) or benzylamine (Miller and Alexander 1991), which have water solubilities of 900 mg l)1 and 1 kg l)1, respectively (Howard and Meyln 1997). However, a study by Park et al. (2001) showed that bacteria are able to utilize both sorbed and nonsorbed 2,4-D through rate calculations based on the liquid-phase concentration of 2,4-D. This is, therefore, in (Askari and Pollard 2005) direct conflict to the original study by Ogram et al. (1985), who used mathematical models based on laboratory data to show that sorbed 2,4-D was unavailable and not degraded by ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 1243 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License J.L. Stroud et al. micro-organisms, and only the solution phase 2,4-D was degraded. Additionally, the chemicals 2,4-D and benzylamine are up to 1Æ11 · 109 more water-soluble than hexadecane, and up to 9Æ09 · 105 times more watersoluble than phenanthrene (Table 1). Hydrocarbons are considered to be poorly water-soluble organic contaminants; yet this is relative; for example, naphthalene and phenanthrene are 33 000 and over 1200 times more water-soluble than hexadecane. This raises several issues when comparing the bioaccessibility and biodegradation of aromatic and aliphatic hydrocarbons in soil. i Is the emphasis on the aqueous phase and passive uptake actually pertinent to the very low water soluble hydrocarbons? ii Does the readily desorbed fraction adequately describe the size of a bioaccessible fraction? iii Are there different modes of biodegradation? These questions are addressed in Fig. 2, in which (a) illustrates the simple mass transfer and mass transport of a relatively water-soluble chemical, benzylamine, which is not limited by low availability; (b) illustrates the mass transport limitations of a poorly water-soluble hydrocarbon (naphthalene); (c) shows that the biodegradation rate of phenanthrene is controlled by the rate of dissolution, and (d and e) illustrate the specialized mechanisms that bacteria have to degrade HOCs, such as hexadecane, enabling them to overcome the low contaminant bioaccessibility. The degree of biodegradation of aliphatic hydrocarbons is typically lower than their aromatic counterparts. For example, Huesemann et al. (2004) carried out a biodegradation study using hydrocarbon contaminated soils inoculated with degraders adapted to use Minas crude oil in slurry reactors. The results showed that, in the Belhaven soil that had an initial 1Æ6% hydrocarbon contamination, less than 20% of the initial concentration of hexadecane remained after 27 d of remediation. The PAH phenanthrene in the same time period had decreased to less than 5%, showing the higher residual fractions of an aliphatic hydrocarbon. Further, a study by Chaineau et al. (1995) investigated the biodegradation of drill cuttings, showing that the concentration of saturated hydrocarbons decreased from 1350 mg TPH kg)1 to about 400 mg TPH kg)1. The aromatic fraction decreased from an initial 600 mg TPH kg)1 to about 200 mg TPH kg)1. Thus, whilst the percentage of biodegradation was similar, double the concentration of saturated hydrocarbons resided in soil after biodegradation. A key study illustrating the degradability of hydrocarbons was carried out by Loser et al. (1999) in which a microporous, sandy soil was spiked with 0Æ3% hexadecane or phenanthrene, and biodegradation was measured to study a pilot scale percolator. The biodegradation experiment was carried out in 1244 J.L. Stroud et al. inoculated shake flasks. The degree of biodegradation of hexadecane was 80%, highly consistent with the degree of biodegradation of the aliphatic fraction found in remediation studies, equating to a residual fraction of 600 mg kg)1. However, the degree of phenanthrene biodegradation was significantly higher (96%) with a residual concentration of only 100 mg kg)1. A range of phenanthrene concentrations was tested, which showed different percentages of biodegradation; nonetheless, a residual concentration was always detected at about 100 mg TPH kg)1. Thus, the aliphatic hydrocarbon had a significantly higher concentration remaining in the soil after biodegradation as compared with phenanthrene, under the same experimental conditions. These results indicate that aliphatic hydrocarbons may be constrained by factors affecting bioaccessibility to a greater extent than PAHs. Although this aliphatic component may be degradable, degradation in soils does not necessarily occur, and can therefore be considered as an important contaminant fraction. The physicochemical properties of the aliphatic hydrocarbon hexadecane show that it is very hydrophobic, and so it extensively partitions into the solid phase. For example, a study by Watts and Stanton (1999) investigated the mineralization of hexadecane sorbed to silica sand in slurries, and showed that 0Æ36% of hexadecane was present in the aqueous phase and that the sorbed phase was not readily desorbed to the aqueous phase. For example, Huesemann et al. (2003, 2004) reported minimal desorption to the aqueous phase by aliphatic hydrocarbons with an XAD-2 extraction, suggesting that there was a minimal accessible fraction available for biodegradation. However, this does not adequately describe the biodegradable fraction, as aliphatic hydrocarbons are widely reported to be extensively biodegraded in studies in both the laboratory and environment (Huesemann 1995; Gogoi et al. 2003; Huesemann et al. 2003, 2004). Biodegradation of aliphatic hydrocarbons has been shown to significantly exceed desorption to the aqueous phase (Thomas et al. 1986; Huesemann et al. 2003, 2004). Liquid culture experiments as well as NAPL-soil investigations have widely reported that the dissolution of HOCs to the aqueous phase cannot account for the biodegradation rate and postulate the presence of specialized uptake mechanisms (Thomas et al. 1986; Goswami and Singh 1991; Huesemann 1995; Huesemann et al. 2003; Rapp and Gabriel-Jurgens 2003; Huesemann et al. 2004). There are a wide range of mechanisms that lead to the biodegradation of hydrocarbons, and are well described by Johnsen and Karlson (2004). Two of the most important mechanisms, solubilization and direct contact, would result in the degradation of the poorly water-soluble hydrocarbons. ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Bioavailability of hydrocarbons in soil Bioavailability of hydrocarbons in soil (a) e.g. Benzylamine (1 kg l –1) at a concentration where water solubility is not exceeded Mass transfer Solubilised substrate (water solubility not exceeded) Simple diffusion into the cell Mass transport –1 (b) e.g. Naphthalene (30 m gl ) at a concentration where water solubility is not exceeded Mass transfer Solubilised substrate (water solubility not exceeded) Simple diffusion into the cell Minimal aqueous phase presence, therefore mass transport limitations Mass transport –1 (c) e.g. Phenanthrene (1·1 mg l ) at a typical concentration (lower solubility) Mass transfer Simple diffusion into the cell Minimal aqueous phase presence, therefore mass transport limitations Rate of uptake dependent on dissolution to aqueous phase (d) e.g. Hexadecane (0·0009 mg l –1) at a typical concentration (lower solubility) Mass transfer Bacterium produced surfactant – enhances solubility (e) Simple diffusion into the cell Minimal aqueous phase presence, therefore mass transport limitations Rate of uptake dependent on dissolution to aqueous phase Microbes have adaptations to overcome limitations e.g. Hexadecane (0·0009 mg l –1) at a typical concentration (lower solubility) Hydrophobic exterior/ biosurfactant production to allow direct contact Mass transfer Biosurfactants also mediate the rate of uptake and movement into cell Biosurfactant mediated uptake into cell to minimise mass transfer limitations Direct contact, therefore minimal mass transport limitations Figure 2 Range of possible bacterial uptake mechanisms for hydrocarbons in soil. Solubilization. It involves the production of biosurfactants by microbes, which increase the concentration of hydrocarbons in the aqueous phase (illustrated in Fig. 2c). The solubilization of hydrocarbons by biosurfactants is widely reported (Goswami and Singh 1991), where higher concentrations of hydrocarbons were found in the aqueous phase than was expected. Bouchez-Naitali et al. (1999) also noted the importance of solubilization while examining the biodegradation of hexadecane by a variety of strains of bacteria. Bai et al. (1997) showed that the solubility of hexadecane in a 500 mg l)1 rhamnolipid solution was 19 mg l)1, showing that the increase of hydrocarbon concentrations in the aqueous phase was significant (illustrated in Fig. 2d). Whyte et al. (1999b) reported that invagination of hydrocarbons occurred, where inclusions of hydrocarbons in cells formed, followed by the uptake. Noordman et al. (2002) reported that the role of rhamnolipids was to mediate the mass ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 1245 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License J.L. Stroud et al. transfer of hexadecane into cells (illustrated in Fig. 2e), causing biodegradation. Direct contact. In direct contact, the bacterial cells adhere to the surface of the hydrocarbon. This is key to biodegradation as shown by Holden et al. (2002), where direct contact was crucial to the degradation of hexadecane by the bacterium under investigation (illustrated in Fig. 2e). Direct contact can be facilitated by biosurfactants and bioemulsifiers produced by the cells that enhance adhesion between the cell wall and the accessible hydrocarbon (Bouchez-Naitali et al. 1999). For example, the Gram-negative bacterium Acinetobacter spp. (Margesin et al. 2003) is widely reported to produce biosurfactants ⁄ bioemulsifiers; thus, it has a hydrophobic exterior to allow cellular contact with the hydrocarbon. Additionally, some bacteria naturally have hydrophobic cell surfaces enabling cellular adhesion to hydrocarbons (Bouchez-Naitali et al. 1999; Whyte et al. 1999b). Bacteria capable of utilizing sorbed contaminants are widely reported for a range of hydrocarbons, such as naphthalene (Guerin and Boyd 1992) and phenanthrene (Laor et al. 1996; Tang et al. 1998). Deziel et al. (1996) showed in a microbiological study based on biodegradation of PAHs that over 40% microbes produced biosurfactants. Thus, whilst the literature has a strong bias towards biodegradation requiring abiotic desorption of HOCs to the aqueous phase prior to biodegradation, a wide range of sorbed hydrocarbons are available to the degraders (Table 2). However, the role of biosurfactants is not always clear; for example, biosurfactants are also produced by bacteria when only a solubilized contaminant is available (Bouchez-Naitali et al. 1999). Furthermore, the biodegradation extent by bacteria that do not J.L. Stroud et al. produce biosurfactants is not enhanced by the presence of biosurfactants, indicating that the role of biosurfactants is species specific (Noordman and Janssen 2002). Additionally, the ability to produce surface active agents does not necessarily correspond to mineralization of PAHs (Willumsen and Karlson 1997). Clearly, more research is required to investigate the role of biosurfactants on hydrocarbon biodegradation in soils. This is particularly important as biodegradation is understood to be the principal mechanism for the removal of aliphatic hydrocarbons from soil and essential for the successful bioremediation of contaminated sites. Bioremediation of hydrocarbons in soil Soils, considered suitable for bioremediation, are typically contaminated with hydrocarbons at levels of 0Æ2–55% by volume of oil concentration (Huesemann et al. 2002). Targets for the remediation of hydrocarbon-contaminated land are currently based upon the total petroleum hydrocarbon (TPH) content (Gogoi et al. 2003), which measures hydrocarbons within the range of C6-C40, although in the UK this would be determined by a risk-based approach based on future intended land use (Askari and Pollard 2005). Bioremediation relies on the breakdown of target pollutant compounds in the soil through microbial degradation, by using either in situ (including strategies involving soil amendment, bioventing ⁄ biosparging, natural attenuation and phyto- ⁄ rhizo-remediation) or ex situ (biopiling, composting, bioreactors and land farming) techniques. The remedy may be achieved by an intense engineered biological solution or by means of a less intensive attenu- Table 2 Studies investigating the uptake and biodegradation of hydrocarbons in soil Chemical Biodegradation and bioavailability mechanism PAHs (e.g. phenanthrene, naphthalene) Soil-sorbed availability Biosurfactant production Hydrophobic cell walls ⁄ Direct contact Aliphatics (e.g. dodecane, hexadecane) Soil-sorbed availability Hydrophobic cell walls ⁄ Direct contact Biosurfactant production HOCs (e.g. biphenyl, styrene) 1246 Hydrocarbon inclusions in cells Hydrophobic cell walls ⁄ Direct contact Soil-sorbed availability Reference Tang et al. 1998 Deziel et al. 1996; Dean et al. 2001; Wick et al. 2001; Wick et al. 2002; Bogan et al. 2003 Guerin and Boyd 1992; Ortega-Calvo and Alexander 1994; Guerin and Boyd 1997; Bastiaens et al. 2000; Holden et al. 2002; Park et al. 2002; Bogan et al. 2003; Johnsen and Karlson 2004 Thomas et al. 1986; Huesemann 1995; Huesemann et al. 2003; 2004 Bouchez-Naitali et al. 1999; Bouchez-Naitali et al. 2001; Holden et al. 2002; Bogan et al. 2003 Goswami and Singh 1991; Zhang and Miller 1995; Herman et al. 1997; Bouchez-Naitali et al. 1999; Barathi and Vasudevan 2001; Noordman and Janssen 2002; Noordman et al. 2002; Bogan et al. 2003; Gogoi et al. 2003; Rapp and Gabriel-Jurgens 2003 Scott and Finnerty 1976a,b; Whyte et al. 1999b Calvillo and Alexander 1996; Feng et al. 2000 Fu et al. 1994 ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Bioavailability of hydrocarbons in soil ation stage. The selection of a method is often driven by economics. Currently, for example, (monitored) natural attenuation accounts for over one-quarter of all petroleum contaminated land bioremediation strategies in the USA (Holden et al. 2002). In some cases, the physicochemical and biological constraints of a remediation project negate the selection of an attenuation approach and a bioengineered solution is required. Such techniques may be selected when there is low microbial catabolic activity, a lack of available nutrients, poor pollutant bioavailability, pH extremes or soil physical factors. A slow degradation rate is unsuitable from a regulatory perspective, and enhanced bioremediation techniques have been developed to speed up degradation. To ensure optimal biological performance, it is common to manipulate the degrading microbial populations and the environment. Several general approaches can be applied: (i) environmental modification, (ii) bioaugmentation and (iii) enhancement of bioavailability. Environmental modification involves the manipulation of the physicochemical nature of the contaminated soil by altering pH, O2, H2O, and ⁄ or nutrient levels. Nutrient deficiencies can occur due to the enrichment of carbon caused by the pollution event (Smith et al. 1998). The optimization of the C : N : P ratio is thought to be one of the most important amendments enhancing the biodegradation rate and extent (Smith et al. 1998). However, whilst these nutrients are routinely added, biostimulation has been found to be inconsistent. Inorganic nutrients (fertilizers) are the most widely used amendment, and success has been reported (Lin and Mendelssohn 1998; Whyte et al. 2001; Trindade et al. 2005; Ayotamuno et al. 2006; Perfumo et al. 2007). For example, Ayotamuno et al. (2006) found that the addition of NPK fertilizer to a polluted agricultural soil in Nigeria had significantly enhanced the biodegradation rate of the crude oil, initially present at 84 mg TPH kg)1 and reduced by 50–95% in the test cells. However, the traditional addition of fertilisers or urea has been shown to have no affect (Nyman 1999; Ruberto et al. 2003; Bento et al. 2005; Sarkar et al. 2005; Fernandez-Alvarez et al. 2006; Sabate et al. 2006). This traditional application has been found to have a negative impact on bacteria (Sarkar et al. 2005) and fungi (Chaillan et al. 2006), and thus may significantly inhibit biodegradation. Sarkar et al. (2005) reported that fertilizer addition caused either NH3 overdosing and ⁄ or fertilizerinduced acid toxicity, which significantly affected the microbial community. Chaillan et al. (2006) found that the addition of urea had a fungicidal effect and caused a toxic concentration of ammonia gas, significantly limiting the degradation extent of soil contaminated with weathered oils and drill cuttings. Thus, alternative methods of nutrient amendment to these traditional applications were Bioavailability of hydrocarbons in soil receiving increased research attention. A novel technique involves the application of biosolids, which are cheap and widely available from sewage treatment works, and have a slow release of highly available nutrients, avoiding the problems associated with traditional applications (Sarkar et al. 2005). A study by Sarkar et al. (2005) compared the traditional fertilizer addition and biosolids application and monitored natural attenuation on Tarpley clay soil contaminated with 3500 mg TPH kg)1 diesel. The results showed that, after 8 weeks of incubation, the biosolid amended conditions showed a superior TPH reduction of 96%. Further, the traditional fertilizer application exerted toxic effects on the soil microflora, while the biosolid amendment showed no such impacts. Bioaugmentation involves the addition of an enriched degrading microbial inoculum to remove target contaminant molecules. However, the success of applying commercially available microbes is limited (Jones 1998; Whyte et al. 1999a). Bioaugmentation research is developing into two distinct approaches: (i) environmental specificity and (ii) microbe specificity. The main limitation in commercial preparations and laboratory based inocula is the inability to rapidly adapt to the local field conditions (Vogel 1996). Environmentally-specific bioaugmentation can be defined as the use of naturally adapted indigenous microbes that have been cultured and enriched in the laboratory and then applied back to the local contaminated soil. This approach has shown considerable success. For example, Bento et al. (2005) showed up to four-fold increase in the microbial activity of bioaugmented diesel-contaminated soils. This corresponded with differences in the degradation extent; for example, the light hydrocarbon fraction (C12-C23) degradation showed 48Æ7 ± 0Æ33% in the naturally attenuated treatment as compared with 75Æ2 ± 0Æ17% in the bioaugmented treatment. In the heavy hydrocarbon fraction (C23-C40), 45Æ7 ± 0Æ41% degradation was found in the biostimulated condition as compared with 72Æ7 ± 0Æ37% degradation in the bioaugmented condition using Long Beach soil, initially contaminated with 2800 mg TPH kg)1 TPH (C12-C23) and 9450 mg TPH kg)1 TPH (C23-C40). In terms of microbe specificity, a new approach is the molecular engineering of microbes to produce highly effective degrading microbes as reviewed by Ang et al. (2005). This report identifies that research has focussed on enhancing the presence of enzymes that cause PAH biodegradation, such as laccases and cytochrome P450 oxidases, through either rational design or directed evolution to produce highly effective degrading organisms (Ang et al. 2005). This research is in its infancy, with the focus on the complex procedure of genetically modifying organisms and currently little practical application to biodegradation. Nonetheless, whilst there are obvious advan- ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 1247 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License J.L. Stroud et al. tages of producing efficient degrading organisms, the field application of genetically modified organisms is improbable given the current environmental regulations and increasing unpopularity with the general public. Enhancing the bioavailability of organic contaminants may also be used in the bioremediation of contaminated land. For example, heat has been used to enhance the removal of aliphatic hydrocarbons from soil; Perfumo et al. (2007) reported that indigenous thermophilic bacteria are common hydrocarbon degraders and that bioremediation at 60C showed significant hexadecane intrinsic degradation. Soil was amended with 2% (w ⁄ v) hexadecane; after 40 d, 70% degradation was measured in microcosms maintained at 60C. However, hexadecane degradation was only approximately 38% in soil microcosms maintained at room temperature. Furthermore, with the boiling point of hexadecane being 287C, losses are unlikely to have been due to volatilization. This enhanced degradation is hypothesized to be caused by the mobilization and solubilization of hexadecane at a higher temperature as well as the stimulation of thermophilic degrading microorganisms. Chemical surfactants are able to emulsify or pseudosolubilize poorly water-soluble compounds and, as such, enhance bioavailability. Attributes such as charge, hydrophilic balance and micellar concentrations define the performance and applicability of the surfactant (van Hamme et al. 2003), and the enhancement of bioavailability can be easily measured (Efroymson and Alexander, 1991). Although widely used in industrial processing applications, surfactants are more difficult to apply to soils where there may be significant forms of carbon present other than just the hydrocarbons of interest. For example, Mulligan et al. (2001), on reviewing the most significant findings in the literature, reported that degradation of poorly soluble hydrocarbons could be inhibited because of toxicity associated with the surfactants, preferential metabolism of the surfactant, cellular membrane interference and ⁄ or reduced hydrocarbon bioavailability. Rouse et al. (1994) also observed the potential application of these chemicals in wastewater and slurry applications, but were critical about their applicability to oil contaminated soils. Indeed, it was further stressed that many surfactants are designed to operate independent of microbial degradation, and thus such combined degradative capacity may be an exception rather than a rule. Of wider application is biosurfactant enhanced remediation. Many biological molecules are amphiphilic and hence could partition at interphases. Microbial compounds that exhibit particularly high surface activity and emulsifying activities are classified as biosurfactants, which include lipopeptides, glycolipids, neutral lipids and fatty acids. Cameotra and Bollag (2003) considered the 1248 J.L. Stroud et al. way in which communities exhibit biosurfactant production, putatively enhancing degradation through increased bioavailability. It was concluded that these structurally diverse compounds produced by hydrocarbon degraders exhibit surface activities that are difficult to produce synthetically. These compounds are also biodegradable and have low microbial toxicity, and their concentration and particular traits are likely to be defined by environmental parameters. Commercial microbial remediation of hydrocarbon and crude oil-contaminated soils is an emerging technology involving the application of biosurfactants (Bartha 1986; Harvey et al. 1990; Banat 1995; Ghosh et al. 1995). Hydrocarbon degradation by indigenous microbial populations is the main mechanism employed (Atlas and Bartha, 1992) because the performance of enhanced degradation through the addition of prepared microbial inocula (bioaugmentation) has been ambiguous (Atlas, 1991). However, the amendment of biosurfactant to stimulate indigenous populations has been shown to degrade hydrocarbons at rates higher than those achievable through nutrient addition alone. For example, rhamnolipids from Pseudomonas aeruginosa were shown to remove substantial quantities of oil from contaminated Alaskan gravel from the Exxon Valdez oil spill (Harvey et al. 1990). Further, Bragg et al. (1994) reported the effectiveness of in situ bioremediation on the Exxon Valdez oil spill using biosurfactant methods in a large-scale experiment. More recently, Van Dyke et al. (1993) demonstrated more than a doubling of hydrocarbon recovery (from 25 to 70% and 40 to 80%) from contaminated soil using rhamnolipids from P. aeruginosa. Glycolipid biosurfactants have also been shown to enhance the hydrocarbon removal (from 80 to 90–95%) from soil; furthermore, the biosurfactant was reported to increase hydrocarbon mineralization by two-fold and shorten the adaptation time of microbial populations to fewer hours (Mulligan and Gibbs, 1993). Conclusion This review discussed the presence, consequence and removal of aliphatic hydrocarbons in soils. Aliphatic hydrocarbons (C14-C20) present in fuels are ubiquitous soil contaminants and are carcinogenic at high concentrations and represent a considerable hazard to biological receptors because of the formation of toxic and carcinogenic metabolites as a result of biodegradation. Aliphatic hydrocarbon biodegradation is constitutive to the indigenous microbial community, which have specialized uptake degradation mechanisms that enable sorbed-phase degradation. However, significant concentrations of aliphatics persist in soils because of their interaction with ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Bioavailability of hydrocarbons in soil soil components resulting in bioavailability limitations. Remediation techniques attempt to enhance the removal of aliphatic hydrocarbons from soils, through modifications to the microbial community, enhanced biostimulation and increasing bioavailability using cyclodextrin amendments. The success of these techniques is important given the nature, consequences and bioavailability limitations associated with aliphatic hydrocarbon contamination in soils. Acknowledgements The authors would like to thank the Natural Environment Research Council, UK and Remedios, for financially supporting this work. References Alexander, M. (2000) Aging, bioavailability, and overestimation of risk from environmental pollutants. Environ Sci Technol 34, 4259–4265. Ang, E.L., Zhao, H. and Obbard, J.P. (2005) Recent advances in the bioremediation of persistent organic pollutants via biomolecular engineering. Enzyme Microb Technol 37, 487–496. Askari, K. and Pollard, S. (2005) The UK approach for evaluating human health risks from petroleum hydrocarbon in soils: Environment Agency. Science Report P5-080 ⁄ TR3. Available at: www.environment-agency.gov.uk. Atlas, R.M. (1991) Microbial hydrocarbon degradation – bioremediation of oil spills. J Chem Technol Biotechnol 52, 149–156. Atlas, R.M. and Bartha, R. (1992) Hydrocarbon biodegradation and oilspill bioremediation. Advances Microb Ecol 12, 287– 338. Ayotamuno, M.J., Kogbara, R.B., Ogaji, S.O.T. and Probert, S.D. (2006) Bioremediation of a crude-oil polluted agricultural-soil at Port Harcourt, Nigeria. Appl Energy 83, 1249– 1257. Bai, G.Y., Brusseau, M.L. and Miller, R.M. (1997) Biosurfactant-enhanced removal of residual hydrocarbon from soil. J Contam Hydrol 25, 157–170. Banat, I.M. (1995) Characterization of biosurfactants and their use in pollution removal – state of the art. Acta Biotechnologica 15, 251–267. Barakat, A.O., Mostafa, A.R., Rullkötter, J. and Rahman Hegazi, A. (1999) Application of a multimolecular marker approach to fingerprint petroleum pollution in the marine environment. Mar Pollut Bull 38, 535–544. Barathi, S. and Vasudevan, N. (2001) Utilization of petroleum hydrocarbons by Pseudomonas fluorescens isolated from a petroleum-contaminated soil. Environ Int 26, 413–416. Bartha, R. (1986) Biotechnology of petroleum pollutant biodegradation. Microb Ecol 12, 155–172. Bioavailability of hydrocarbons in soil Bastiaens, L., Springael, D., Wattiau, P., Harms, H., deWachter, R., Verachtert, H. and Diels, L. (2000) Isolation of adherent polycyclic aromatic hydrocarbon (PAH)-degrading bacteria using PAH-sorbing carriers. Appl Environ Microbiol 66, 1834–1843. Bento, F.M., Camargo, F.A.O., Okeke, B.C. and Frankenberger, W.T. (2005) Comparative bioremediation of soils contaminated with diesel oil by natural attenuation, biostimulation and bioaugmentation. Bioresour Technol 96, 1049– 1055. Block, R., Allworth, N. and Bishop, M. (1991) Assessment of diesel contamination in soil. In Hydrocarbon contaminated soils, Vol I Remediation Techniques, Environmental Fate, Risk Assessment, Analytical Methodologies, Regulatory Considerations ed. Calabrese, E. and Kostecki, P. pp. 135–148. Chelsea, MI: Lewis Publishers. Bogan, B.W., Lahner, L.M., Sullivan, W.R. and Paterek, J.R. (2003) Degradation of straight-chain aliphatic and highmolecular- weight polycyclic aromatic hydrocarbons by a strain of Mycobacterium austroafricanum. J Appl Microbiol 94, 230–239. Bouchez-Naitali, M., Rakatozafy, H., Marchal, R., Leveau, J.Y. and Vandecasteele, J.P. (1999) Diversity of bacterial strains degrading hexadecane in relation to the mode of substrate uptake. J Appl Microbiol 86, 421–428. Bouchez-Naitali, M., Blanchet, D., Bardin, V. and Vandecasteele, J.P. (2001) Evidence for interfacial uptake in hexadecane degradation by Rhodococcus equi: the importance of cell flocculation. Microbiology (UK) 147, 2537–2543. Bragg, J.R., Prince, R.C., Harner, E.J. and Atlas, R.M. (1994) Effectiveness of bioremediation for the Exxon Valdez oil spill. Nature 368, 413–418. Britton, L.N. (1984) Microbial degradation of aliphatic hydrocarbons. In Microbial Degradation of Organic Compounds ed. Gibson, D.T. pp. 89–129. USA: Marcel Dekker Inc. Calvillo, Y.M. and Alexander, M. (1996) Mechanism of microbial utilisation of biphenyl sorbed to polyacrylic beads. Appl Microbiol Biotechnol 45, 383–390. Cameotra, S.S. and Bollag, J.-M. (2003) Biosurfactantenhanced bioremediation of PAHs. Crit Rev Environ Sci Technol 30, 111–126. Chaillan, F., Chaineau, C.H., Point, V., Saliot, A. and Oudot, J. (2006) Factors inhibiting bioremediation of soil contaminated with weathered oils and drill cuttings. Environ Pollut 144, 255–265. Chaineau, C.H., Morel, J.L. and Oudot, J. (1995) Microbialdegradation in soil microcosms of fuel-oil hydrocarbons from drilling cuttings. Environ Sci Technol 29, 1615–1621. Chayabutra, C. and Ju, L.K. (2000) Degradation of n-hexadecane and its metabolites by Pseudomonas aeruginosa under microaerobic and anaerobic denitrifying conditions. Appl Environ Microbiol 66, 493–498. Cole, G.M. (1994) Assessment and Remediation of Petroleum Contaminated Sites. Boca Raton: Lewis Publishers. ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 1249 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License J.L. Stroud et al. Cornelissen, G., Van Noort, P.C.M. and Govers, H.A.J. (1997) Desorption kinetics of chlorobenzenes, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls: sediment extraction with tenax and effects of contact time and solute hydrophobicity. Environ Toxicol Chem 16, 1351–1357. Cornelissen, G., van Noort, P.C.M. and Govers, H.A.J. (1998) Mechanism of slow desorption of organic compounds from sediments: A study using model sorbents. Environ Sci Technol 32, 3124–3131. Cornelissen, G., Gustafsson, O., Bucheli, T.D., Jonker, M.T.O., Koelmans, A.A. and Van Noort, P.C.M. (2005) Extensive sorption of organic compounds to black carbon, coal, and kerogen in sediments and soils: mechanisms and consequences for distribution, bioaccumulation, and biodegradation. Environ Sci Technol 39, 6881–6895. Dean, S.M., Jin, Y., Cha, D.K., Wilson, S.V. and Radosevich, M. (2001) Phenanthrene degradation in soils co-inoculated with phenanthrene-degrading and biosurfactant-producing bacteria. J Environ Qual 30, 1126–1133. Dew, N.M., Paton, G.I. and Semple, K.T. (2005) Prediction of [3-14C]phenyldodecane biodegradation in cable insulating oil-spiked soil using selected extraction techniques. Environ Pollut 138, 316–323. Deziel, E., Paquette, G., Villemur, R., Lepine, F. and Bisaillon, J.G. (1996) Biosurfactant production by a soil Pseudomonas strain growing on polycyclic aromatic hydrocarbons. Appl Environ Microbiol 62, 1908–1912. Doick, K.J., Clasper, P.J., Urmann, K. and Semple, K.T. (2006) Further validation of the HPCD-technique for the evaluation of PAH microbial availability in soil. Environ Pollut 144, 345–354. Efroymson, R.A. and Alexander, M. (1991) Biodegradation by an Arthrobacter species of hydrocarbons partitioned into an organic solvent. Appl Environ Microbiol 57, 1441–1444. Environment Agency (2006) Available at: http://www. environment-agency.gov.uk/commondata/103601/ poll_incidents_2005_1438766.xls. Feng, Y., Park, J.-H., Voice, T.C. and Boyd, S.A. (2000) Bioavailability of soil-sorbed biphenyl to bacteria. Environ Sci Technol 34, 1977–1984. Fernandez-Alvarez, P., Vila, J., Garrido-Fernandez, J.M., Grifoll, M. and Lema, J.M. (2006) Trials of bioremediation on a beach affected by the heavy oil spill of the Prestige. J Hazard Mater 137, 1523–1531. Fu, M.H., Mayton, H. and Alexander, M. (1994) Desorption and biodegradation of sorbed stryene in soil and aquifer soilds. Environ Toxicol Chem 13, 749–753. Ghosh, M.M., Yeom, I.T., Shi, Z., Cox, C.D. and Robinson, K.G. (1995) Surfactant-enhanced bioremediation of PAHand PCB-contaminated soils. In Third International in situ and On-Site Bioreclamation Symposium ed. Hinchee, R.E., Vogel, C.M. and Brockman, F.J. pp. 15–23. Columbus, OH: Battelle Press. Gogoi, B.K., Dutta, N.N., Goswami, P. and Mohan, T.R.K. (2003) A case study of bioremediation of petroleum- 1250 J.L. Stroud et al. hydrocarbon contaminated soil at a crude oil spill site. Adv Environ Res 7, 767–782. Goswami, P. and Singh, H.D. (1991) Different modes of hydrocarbon uptake by two Pseudomonas species. Biotechnol Bioeng 37, 1–11. Grishchenkov, V.G., Townsend, R.T., McDonald, T.J., Autenrieth, R.L., Bonner, J.S. and Boronin, A.M. (2000) Degradation of petroleum hydrocarbons by facultative anaerobic bacteria under aerobic and anaerobic conditions. Process Biochem 35, 889–896. Guerin, W.F. and Boyd, S.A. (1992) Differential bioavailability of soil-sorbed naphthalene to two bacterial species. Appl Environ Microbiol 58, 1142–1152. Guerin, W.F. and Boyd, S.A. (1997) Bioavailability of naphthalene associated with natural and synthetic sorbents. Water Res 31, 1504–1512. van Hamme, J.D., Singh, A. and Ward, O.P. (2003) Recent advances in petroleum microbiology. Microbiol Mol Biol Rev 67, 503–549. Harvey, S., Elashvili, I., Valdes, J.J., Kamely, D. and Chakrabarty, A.M. (1990) Enhanced removal of Exxon Valdez spilled oil from Alaskan gravel by a microbial surfactant. Biotechnology 8, 228–230. Hatzinger, P.B. and Alexander, M. (2005) Effect of ageing of chemicals in soil on their biodegradability and extractability. Environ Sci Technol 29, 537–545. Heider, J., Spormann, A.M., Beller, H.R. and Widdel, F. (1999) Anaerobic bacterial metabolism of hydrocarbons. FEMS Microbiol Rev 22, 459–473. Herman, D.C., Lenhard, R.J. and Miller, R.M. (1997) Formation and removal of hydrocarbon residual in porous media: effects of attached bacteria and biosurfactants. Environ Sci Technol 31, 1290–1294. Holden, P.A., LaMontagne, M.G., Bruce, A.K., Miller, W.G. and Lindow, S.E. (2002) Assessing the role of Pseudomonas aeruginosa surface-active gene expression in hexadecane biodegradation in sand. Appl Environ Microbiol 68, 2509–2518. Howard, P.H. and Meyln, W.M.E. (1997) Handbook of Physical Properties of Organic Chemicals. Boca Raton: CRC Press Inc. Huesemann, M.H. (1995) Predictive model for estimating the extent of petroleum hydrocarbon biodegradation in contaminated soils. Environ Sci Technol 29, 7–18. Huesemann, M.H., Hausmann, T.S. and Fortman, T.J. (2002) Microbial factors rather than bioavailability limit the rate and extent of PAH biodegradation in aged crude oil contaminated model soils. Bioremediation J 6, 321–336. Huesemann, M.H., Hausmann, T.S. and Fortman, T.J. (2003) Assessment of bioavailability limitations during slurry biodegradation of petroleum hydrocarbons in aged soils. Environ Toxicol Chem 22, 2853–2860. Huesemann, M.H., Hausmann, T.S. and Fortman, T.J. (2004) Does bioavailability limit biodegradation? A comparison of hydrocarbon biodegradation and desorption rates in aged soils Biodegradation 15, 261–274. ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Bioavailability of hydrocarbons in soil Johnsen, A.R. and Karlson, U. (2004) Evaluation of bacterial strategies to promote bioavailability of polycylic aromatic hydrocarbons. Appl Microbiol Biotechnol 63, 452–459. Jones, W.R. (1998) Practical applications of marine bioremediation. Curr Opin Biotechnol 9, 300–304. Kelsey, J.W., Kottler, B.D. and Alexander, M. (1997) Selective chemical extractants to predict bioavailability of soil-aged organic chemicals. Environ Sci Technol 31, 214–217. Koma, D., Hasumi, F., Yamamoto, E., Ohta, T., Chung, S.Y. and Kubo, M. (2001) Biodegradation of long-chain nparaffins from waste oil of car engine by Acinetobacter sp. J Biosci Bioeng 91, 94–96. Laor, Y., Strom, P.F. and Farmer, W.J. (1996) The effect of sorption on phenanthrene bioavailability. J Biotechnol 51, 227–234. Lin, Q. and Mendelssohn, I.A. (1998) The combined effects of phytoremediation and biostimulation in enhancing habitat restoration and oil degradation of petroleum contaminated wetlands. Ecol Eng 10, 263–274. Liste, H.-H. and Alexander, M. (2002) Butanol extraction to predict bioavailability of PAHs in soil. Chemosphere 46, 1011–1017. Loser, C., Seidel, H., Hoffmann, P. and Zehnsdorf, A. (1999) Bioavailability of hydrocarbons during microbial remediation of a sandy soil. Appl Microbiol Biotechnol 51, 105–111. Macleod, C.J.A. and Semple, K.T. (2000) Influence of contact time on extractability and degradation of pyrene in soils. Environ Sci Technol 34, 4952–4957. Macleod, C.J.A. and Semple, K.T. (2003) Sequential extraction of low concentrations of pyrene and formation of nonextractable residues in sterile and non- sterile soils. Soil Biol Biochem 35, 1443–1450. Maier, R.M., Pepper, I.L. and Gerba, C.P. (2000) Environmental Microbiology. San Diego: Academic Press. Margesin, R., Labbe, D., Schinner, F., Greer, C.W. and Whyte, L.G. (2003) Characterization of hydrocarbon-degrading microbial populations in contaminated and pristine alpine soils. Appl Environ Microbiol 69, 3085–3092. Miller, M.E. and Alexander, M. (1991) Kinetics of bacterialdegradation of benzylamine in a montmorillonite suspension. Environ Sci Technol 25, 240–245. Morgan, P. and Watkinson, R.J. (1994) Biodegradation of components of petroleum. In Biochemistry of Microbial Degradation ed. Ratledge, C. pp. 1–31. Netherlands: Kluwer Academic Publishers. Mulligan, C.N. and Gibbs, B.F. (1993) Factors influencing the economics of biosurfactants. In Biosurfactants: Production, Properties, Applications ed. Kosaric, N. pp. 329–371. New York, NY: Marcel Dekker Inc. Mulligan, C.N., Yong, R.N. and Gibbs, B.F. (2001) Surfactant enhanced remdiation of contaminated soil: a review. Eng Geol 60, 371–380. Noordman, W.H. and Janssen, D.B. (2002) Rhamnolipid stimulates uptake of hydrophobic compounds by Pseudomonas aeruginosa. Appl Environ Microbiol 68, 4502–4508. Bioavailability of hydrocarbons in soil Noordman, W.H., Wachter, J.H.J., de Boer, G.J. and Janssen, D.B. (2002) The enhancement by surfactants of hexadecane degradation by Pseudomonas aeruginosa varies with substrate availability. J Biotechnol 94, 195–212. Nyman, J.A. (1999) Effect of crude oil and chemical additives on metabolic activity of mixed microbial populations in fresh marsh soils. Microb Ecol 2, 152–162. Ogram, A.V., Jessup, R.E., Oui, L.T. and Rao, P.S.C. (1985) Effects of sorption on biological degradation rates of (2,4- dichlorophenoxy)acetic acid in soils. Appl Environ Microbiol 49, 582–587. Ortega-Calvo, J.J. and Alexander, M. (1994) Roles of bacterial attachment and spontaneous partitioning in the biodegradation of napthalene initially present in nonaqueous-phase liquids. Appl Environ Microbiol 60, 2643–2646. Page, D.S., Foster, J.C., Fickett, P.M. and Gilfillan, E.S. (1988) Identification of petroleum sources in an area impacted by the Amoco Cadiz oil spill. Mar Pollut Bull 19, 107–115. Pan, B., Xing, B.S., Liu, W.X., Tao, S., Lin, X.M., Zhang, X.M., Zhang, Y.X., Xiao, Y., et al. (2006) Distribution of sorbed phenanthrene and pyrene in different humic fractions of soils and importance of humin. Environ Pollut 143, 24–33. Park, J.H., Kay, D., Zhao, X.D., Boyd, S.A. and Voice, T.C. (2001) Kinetic modeling of bioavailability for sorbed-phase 2,4-dichlorophenoxyacetic acid. J Environ Qual 30, 1523– 1527. Park, J.H., Zhao, X.D. and Voice, T.C. (2002) Development of a kinetic basis for bioavailability of sorbed naphthalene in soil slurries. Water Res 36, 1620–1628. Perfumo, A., Banat, I.M., Marchant, R. and Vezzulli, L. (2007) Thermally enhanced approaches for bioremediation of hydrocarbon-contaminated soils. Chemosphere 66, 179– 184. Pignatello, J.J. and Xing, B. (1996) Mechanisms of slow sorption of organic chemicals to natural particles. Environ Sci Technol 30, 1–11. Pignatello, J., Martinson, M., Steiert, J., Carlson, R. and Crawford, R. (1983) Biodegradation and photolysis of pentachlorophenol in artificial freshwater streams. Appl Environ Microbiol 46, 1024–1031. Rapp, P. and Gabriel-Jurgens, L.H.E. (2003) Degradation of alkanes and highly chlorinated benzenes, and production of biosurfactants, by a psychrophilic Rhodococcus sp and genetic characterization of its chlorobenzene dioxygenase. Microbiology (UK) 149, 2879–2890. Reid, B.J., Jones, K.C. and Semple, K.T. (2000a) Bioavailability of persistent organic pollutants in soils and sediments – a perspective on mechanisms, consequences and assessment. Environ Pollut 108, 103–112. Reid, B.J., Stokes, J.D., Jones, K.C. and Semple, K.T. (2000b) Nonexhaustive cyclodextrin-based extraction technique for the evaluation of PAH bioavailability. Environ Sci Technol 34, 3174–3179. Reid, B.J., MacLeod, C.J.A., Lee, P.H., Morriss, A.W.J., Stokes, J.D. and Semple, K.T. (2001) A simple 14C-respirometric ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 1251 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License J.L. Stroud et al. method for assessing microbial catabolic potential and contaminant bioavailability. FEMS Microbiol Lett 196, 141–146. Ripley, M.B., Harrison, A.B., Betts, W.B. and Dart, R.K. (2002) Mechanisms for enhanced biodegradation of petroleum hydrocarbons by a microbe-colonized gas-liquid foam. J Appl Microbiol 92, 22–31. Rouse, J.D., Sabatini, D.A., Suflita, J.M. and Harwell, J.H. (1994) Influence of surfactants on microbial degradation of organic contaminants. Crit Rev Microbiol 24, 325–370. Ruberto, L., Vazquez, S.C. and Mac Cormack, W.P. (2003) Effectiveness of the natural bacterial flora, biostimulation and bioaugmentation on the bioremediation of a hydrocarbon contaminated Antarctic soil. Int Biodeterior Biodegradation 52, 115–125. Sabate, J., Vinas, M. and Solanas, A.M. (2006) Bioavailability assessment and environmental fate of polycyclic aromatic hydrocarbons in biostimulated creosote-contaminated soil. Chemosphere 63, 1648–1659. Sarkar, D., Ferguson, M., Datta, R. and Birnbaum, S. (2005) Bioremediation of petroleum hydrocarbons in contaminated soils: comparison of biosolids addition, carbon supplementation, and monitored natural attenuation. Environ Pollut 136, 187–195. Schwarzenbach, R.P. and Westall, J. (1981) Transport of nonpolar organic compounds from surface water to groundwater. Laboratory sorption studies. Environ Sci Technol 15, 1360–1367. Scott, C.C.L. and Finnerty, W.R. (1976a) Characterisation of intracytoplamic hydrocarbon inclusions from the hydrocarbon oxidising Acinetobacter species HO-1 N. J Bacteriol 127, 481–489. Scott, C.C.L. and Finnerty, W.R. (1976b) A comparative analysis of the ultrastructure of hydrocarbon-oxidising microorganisms. J Gen Microbiol 94, 342–350. Semple, K.T., Morris, A.W.J. and Paton, G.I. (2003) Bioavailability of hydrophobic organic contaminants in soils: fundamental concepts and techniques for analysis. European J Soil Sci 564, 1–10. Semple, K.T., Doick, K.J., Jones, K.C., Burauel, P., Craven, A. and Harms, H. (2004) Defining bioavailability and bioaccessibility of contaminated soil and sediment is complicated. Environ Sci Technol 38, 228A–231A. Sepic, E., Leskovsek, H. and Trier, C. (1995) Aerobic bacterialdegradation of selected polyaromatic compounds and nalkanes found in petroleum. J Chromatogr A 697, 515–523. Smith, V.H., Graham, D.W. and Cleland, D.D. (1998) Application of resource-ratio theory to hydrocarbon biodegradation. Environ Sci Technol 32, 3386–3395. Speight, J.G. (1999) The Chemistry and Technology of Petroleum. New York: Marcel Dekker Inc. Stokes, J.D., Wilkinson, A., Reid, B.J., Jones, K.C. and Semple, K.T. (2005) Prediction of polycyclic aromatic hydrocarbon biodegradation in contaminated soils using an aqueous hydroxypropyl-beta-cyclodextrin extraction technique. Environ Toxicol Chem 24, 1325–1330. 1252 J.L. Stroud et al. Tang, W.-C., White, J.C. and Alexander, M. (1998) Utilisation of sorbed compounds by microorganisms specifically isolated for that purpose. Appl Microbiol Biotechnol 49, 117–121. Thomas, J.M., Yordy, J.R., Amador, J.A. and Alexander, M. (1986) Rates of dissolution and biodegradation of waterinsoluble organic compounds. Appl Environ Microbiol 52, 290–296. Trindade, P.V.O., Sobral, L.G., Rizzo, A.C.L., Leite, S.G.F. and Soriano, A.U. (2005) Bioremediation of a weathered and a recently oil-contaminated soils from Brazil: a comparison study. Chemosphere 58, 515–522. Van Dyke, M.I., Couture, P., Brauer, M., Lee, H. and Trevors, J.T. (1993) Pseudomonas aeruginosa UG2 rhamnolipid biosurfactants: structural characterization and their use in removing hydrophobic compounds from soil. Can J Microbiol 39, 1071–1078. Verschueren (1983) Handbook of Environmental Data on Organic Chemicals, 2nd edn. New York: van Nostrand Reinhold Company Inc. Vogel, T.M. (1996) Bioaugmentation as a soil bioremediation approach. Curr Opin Biotechnol 7, 311–316. Wang, Z., Stout, S.A. and Fengas, M. (2006) Forensic fingerprinting of biomarkers for oil spill characterisation and source identification. Environ Forensics 7, 105–146. Watts, R.J. and Stanton, P.C. (1999) Mineralization of sorbed and NAPL-phase hexadecane by catalyzed hydrogen peroxide. Water Res 33, 1405–1414. Whyte, L.G., Bourbonniere, L.G., Bellerose, C.G. and Greer, C.W. (1999a) Bioremediation assessment of hydrocarboncontaminated soils from the high Arctic. Bioremediation J 3, 69–80. Whyte, L.G., Slagman, S.J., Pietrantonio, F., Bourbonniere, L., Koval, S.F., Lawrence, J.R., Inniss, W.E. and Greer, C.W. (1999b) Physiological adaptations involved in alkane assimilation at a low temperature by Rhodococcus sp strain Q15. Appl Environ Microbiol 65, 2961–2968. Whyte, L.G., Goalen, B., Hawari, J., Labbe, D., Greer, C.W. and Nahir, M. (2001) Bioremediation treatability assessment of hydrocarbon-contaminated soils from Eureka, Nunavut. Cold Reg Sci Tech 32, 121–132. Wick, L.Y., Colangelo, T. and Harms, H. (2001) Kinetics of mass transfer-limited bacterial growth on solid PAHs. Environ Sci Technol 35, 354–361. Wick, L.Y., de Munain, A.R., Springael, D. and Harms, H. (2002) Responses of Mycobacterium sp LB501T to the low bioavailability of solid anthracene. Appl Microbiol Biotechnol 58, 378–385. Widdel, F. and Rabus, R. (2001) Anaerobic biodegradation of saturated and aromatic hydrocarbons. Curr Opin Biotechnol 12, 259–276. Wilkes, H., Kühner, S., Bolm, C., Fischer, T., Classen, A., Widdel, F. and Rabus, R. (2003) Formation of n-alkane and cycloalkane-derived organic acids during anaerobic growth of a denitrifying bacterium with crude oil. Org Geochem 34, 1313–1323. ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Bioavailability of hydrocarbons in soil Willumsen, P.A. and Karlson, U. (1997) Screening of bacteria, isolated from PAH-contaminated soils, for production of biosurfactants and bioemulsifiers. Biodegradation 7, 415– 423. Wodzinski, R.S. and Coyle, J.E. (1974) Physical state of phenanthrene for utilization by bacteria. Appl Microbiol 27, 1081–1084. Woo, S.H., Lee, M.W. and Park, J.A. (2004) Biodegradation of phenanthrene in soil-slurry systems with different mass transfer regimes and soil contents. J Biotechnol 110, 235– 250. Xing, B. and Pignatello, J.J. (1996) Time-dependent isotherm shape of organic compounds in soil organic matter: impli- Bioavailability of hydrocarbons in soil cations for sortion mechanism. Environ Toxicol Chem 15, 1282–1288. Zakaria, M.P., Okuda, T. and Takada, H. (2001) Polycyclic aromatic hydrocarbon (PAHs) and hopanes in stranded tar-balls on the coasts of Peninsular Malaysia: applications of biomarkers for identifying sources of oil pollution. Mar Pollut Bull 42, 1357–1366. Zhang, Y.M. and Miller, R.M. (1995) Effect of rhamnolipid (biosurfactant) structure on solubilization and biodegradation of n-alkanes. Appl Environ Microbiol 61, 2247– 2251. ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 102 (2007) 1239–1253 1253 13652672, 2007, 5, Downloaded from https://ami-journals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03401.x by Nigeria Hinari NPL, Wiley Online Library on [14/04/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License J.L. Stroud et al.