Distribution of heavy metals and hydrocarbon contents in an alfisol contaminated with waste-lubricating oil amended with organic wastes

ARTICLE IN PRESS Bioresource Technology xxx (2007) xxx–xxx Distribution of heavy metals and hydrocarbon contents in an alfisol contaminated with waste-lubricating oil amended with organic wastes J.K. Adesodun a a,* , J.S.C. Mbagwu b Department of Soil Science and Land Management, University of Agriculture, P.M.B. 2240, Abeokuta 110001, Ogun-State, Nigeria b Department of Soil Science, University of Nigeria, Nsukka, Enugu-State, Nigeria Received 28 November 2006; received in revised form 24 May 2007; accepted 24 May 2007 Abstract Contamination of soil and groundwater with mineral oil-based products is among the most common sources of pollution in Nigeria. This study evaluated the distribution of some heavy metals and hydrocarbon content in soil contaminated with waste-lubricating oil (spent oil), and the effectiveness of some abundantly available organic wastes from animal source as remediation alternative to the expensive chemical and physical methods. The main-plot treatments include control (C), cow dung (CD), poultry manure (PM) and pig waste (PW) applied at 10 Mg/ha each; while the sub-plot treatments were control (0%), 0.5%, 2.5% and 5% spent oil (SP) applied at 10, 50 and 100 Mg/ha, respectively arranged in a split-plot in Randomized Complete Block Design (RCBD) with four replications. These treatments were applied once each year for two consecutive years. Soil samples (0–20 cm) were collected at 3, 6 and 12 months each year and analyzed for Cr, Ni, Pb and Zn, while the residual total hydrocarbon content (THC) was determined at the end of the 2 years study. Results show significant (p < 0.05) accumulation of these metals with spent oil pollution following the sequence 5%SP > 2.5%SP > 0.5%SP, indicating higher metal pollution with increase in oil pollution. General distribution of Cr, Ni, Pb and Zn, relative to sampling periods, followed 3 months > 6 months > 12 months in the 1st year indicating reduction in metal levels with time. The trend for 2nd year indicated higher accumulation of Cr and Ni in 12 months, while Pb and Zn decreased with time of sampling. The results further showed higher accumulation of Cr followed by Zn, relative to other metals, with oil pollution. However, addition of organic wastes to the oil polluted soils significantly (p < 0.05) led to reduction in the levels of the metals and THC following the order PM > PW > CD.  2007 Elsevier Ltd. All rights reserved. Keywords: Waste-lubricating oil; Heavy metals; Hydrocarbon content; Organic wastes; Soil contamination 1. Introduction The soil is the primary recipient by design or accident of a myriad of waste products and chemicals used in modern industrial society (Brady and Weil, 2002). Contamination of soil and groundwater with petroleum mineral oil and mineral oil-based products is among the most common sources of pollution in Nigeria. The spent oil, otherwise * Corresponding author. Tel.: +234 8033469381. E-mail address: jadesodun@yahoo.com (J.K. Adesodun). called waste-lubricating oil, obtained after servicing and subsequent draining from automobile, generators and industrial machines is disposed off indiscriminately in Nigeria, and adequate attention has not been given to its disposal (Anoliefo and Vwioko, 1995). Analytical procedures commonly used to assess contamination by petroleum products are determination of hydrocarbon fractions, total hydrocarbon and heavy metal contents. The heavy metals and hydrocarbon belong to types of toxic substances that have adverse effects on health. Environment Canada (1996) reported that heavy metals might adversely affect specific tissues, reproduction 0960-8524/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.05.048 Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS 2 J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx and development. This may also cause anemia, nervous system disorders and depressed immune systems, resulting in mortality and effects on population levels (Environment Canada, 1996). Whereas, hydrocarbon contamination exerts adverse effect on soil condition such as higher acidity, reduced C, N, P and exchangeable cations availability, and depressed microbial activity. Industrial wastes containing heavy metals are one of major sources of water pollution (Al-Ashen et al., 1999). The type of metals present in certain waste depends on processes which generated this waste. While Edebiri and Nwanokwale (1981) reported that metals present in spent oil are not necessarily the same as those present in the unused lubricants, Whisman et al. (1974) observed that most heavy metals like Va, Pb, Al, Ni and Fe that are below detection in unused lubricants oil gave high concentration values in used oil. Since Nigeria was reported to account for more than 87 million litres of spent oil waste annually (Anon, 1985), the need to evaluate the risk posed by this pollutant becomes imperative. Remediation approaches are generally classified as physical, chemical and biological. The conventional methods include soil extraction and landfill of the top contaminated soils ex situ is highly effective and clear-cutting (Zhu et al., 2004). This method is often too expensive due to high cost involved in the disposal of the contaminated soil, transportation and backfill of the original site with clean soil (Zhu et al., 2004; Ryan et al., 2001). Hence, in situ bioremediation has been one of the preferred methods for the remediation of petroleum-contaminated site because it is cost-effective and naturally converts the hydrocarbons to harmless byproducts such as carbon dioxide and water. The soil is not transported elsewhere as with landfilling, and easier to scale up to treat large volume of wastes. However, design of in situ bioremediation under specific on-site conditions may remain a challenging issue (Huang et al., 2006). Also, Mohan and Singh (2002) noted that techniques utilizing biological materials, mineral oxides and activated carbon or polymer resins have evolved as options for adsorption of metals which cannot be removed by other techniques. Therefore, this study focused on (i) distribution of some metals (Cr, Ni, Pb and Zn) and total hydrocarbon content (THC) in soil contaminated with varying levels of spent oil and spent oil contaminated soil amended with organic wastes from animal source and (ii) evaluation of differential effectiveness of cow dung (CD), poultry manure (PM) and pig waste (PW) as remediation option. Addition of the organic wastes to some contaminated plots was to serve as nutrients supplement aimed at stimulating biodegradation of this spent oil and to ameliorate the risk of metals from the oil on the environment. The choice of CD, PM and PW was because these wastes are abundantly available in Nigeria, and are cheaper as remediation alternative to the chemical and physical methods that are expensive. 2. Methods 2.1. Site description The experiment was sited at the University of Agriculture, Teaching and Research Farm, Abeokuta, southwestern Nigeria (Lat. 7.12 N and Long. 3.23 E) located within the transition zone of the sub-humid forest to the south and derived savannah to the northwest (Keay, 1959). The soil of this research site is well-drained sandy Table 1 Selected properties of the experimental site, and organic wastes and spent oil applied Parameter Units Soil CD PM PW SPa Sand (2000–50 lm) Silt (50–2 lm) Clay (<2 lm) Texture pH (H2O) OC Total N C:N Average P Ca Mg K Na Exch. Acidity ECEC Crb Nib Pbb Znb g/kg g/kg g/kg 836 48 116 Sandy loam 6.4 8.3 0.71 11.7 7.4 6.09 2.21 1.24 1.13 0.6 11.27 39.5 0.33 6.25 7.11 – – – – 6.7 2.4 0.97 12 126.5 103.4 105.8 0.9 10.5 0.2 – 342 8.9 BD 31.1 – – – – 7.5 39.5 4.0 9.9 143.6 116.8 129.4 1.1 3.6 0.1 – 114.8 28.9 BD 38.6 – – – – – 13.2 1.30 10.2 74.8 75.0 75.8 0.9 3.0 1.2 – 269.7 33.6 BD 121.8 – – – – 5.8 g/kg g/kg – mg/kg cmol/kg cmol/kg cmol/kg cmol/kg cmol/kg cmol/kg mg/kg mg/kg mg/kg mg/kg 30.7 2.66 11.5 0.1 6.5 3.07 240 486 BD = Below determined. a mg/l. b Metal concentrations in soil were determined by Aqua Regia-soluble extraction method, while metals in CD, PM, PW and SP was by extraction with HClO4, HNO3 and H2SO4 method. Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx loam on the surface with gravelly sandy clay loam on the sub-surface derived from basement complex, and classified as Oxic Paleustalf (FDALR, 1990). Selected physical and chemical properties of this site are presented in Table 1. The area has a bimodal rainfall pattern with rains usually commencing in late March or early April and ending in late October or early November with a short dry spell in August. The mean annual rainfall is about 1470 mm with the maximum rainfall in July and September, while the mean monthly temperature range between 28 C and 32 C. 3. Experimental layout A land area of 0.0289 ha was used for this study. The field experimental layout consists of four (4) treatments in each main and sub-plots. The main treatment plots measure 12.25 m2 (3.5 m · 3.5 m), while the sub-plots measure 2.25 m2 (1.5 m · 1.5 m). Each treatment was replicated four times, making a total of 64 plots. The plots were raised beds with guiding borders to prevent spill over between the plots, and they were separated by 50 cm border rows. Organic waste treatments include control (C), cow dung (CD), poultry manure (PM) and pig waste (PW) at 10 Mg/ha (dry matter) each; while the waste-lubricating oil (Rubia S SAE 40), also called spent oil, treatments include control (0%), 0.5%, 2.5% and 5% spent oil (SP) applied at 0, 10, 50 and 100 Mg/ha, respectively. This spent oil was sourced from heavy machines, and each concentration was uniformly applied on the surface of each plot and mixed with the soil. Nutrient supplements (organic wastes) were applied to both the oil polluted and unpolluted plots 7 days after oil treatment. Since addition of oil to soil widens C/N ratio thus making the soil ecosystem unfavourable for microbial species, these organic amendments were applied to augment the soil fertility status, i.e. increase the N and P, thereby narrowing the C/N ratio to encourage the proliferation of microorganisms that could utilize the hydrocarbons as C and N energy sources. All the treatments were applied in a single dose each year for two years. That is, the first year application was in August 2000, while the second application was in October 2001. By the second year, oil contaminated plots had a total spent oil application of 10, 50 and 100 g/kg, respectively, representing total spent oil loading of 1%, 5% and 10% (W/W). 3 5. Laboratory analysis 5.1. Heavy metal concentrations The concentration of heavy metals was determined by Aqua Regia method, as modified by Salt (1998), at the Laboratory of the School of Biological and Environmental Sciences, University of Stirling, Scotland, UK. The procedure involved digestion of 3 g air-dried, pre-sieved (<2 mm), soil samples with 10 ml of concentrated HCl and 3.5 ml of concentrated HNO3 (Analar grade). Every digest batch included 2 blanks and 1 International Atomic Energy Agency (IAEA) reference soil material of known metal concentrations for quality control check. The mixtures were left overnight in the digestion block without heating under the switch-on fume cupboard. The following day, they were heated for 2 h to 140 C, gradually increasing the temperature to control foaming. Distilled water was added to cool the digestates and then filtered with Whatman No. 542 filter paper (pre-washed with 0.5 M HNO3 and wash solution discarded) and topped up to 100 ml with distilled water. The filtrates were analyzed for Cr, Ni, Pb and Zn by flame atomic absorption spectroscopy (FAAS) using a UNICAM 989 AA Spectrophotometer run on SOLAAR software system version 5.28. AAS standards were made up in 2.7 M HCl/0.5 M HNO3 (10 ml HCl and 3.5 ml HNO3 per 100 ml). 5.2. Total hydrocarbon contents Hydrocarbon content of the residual spent oil was determined gravimetrically by toluene extraction (cold extraction) to provide an estimate of total hydrocarbon content (THC). In this procedure, 10 g of soil sample was weighed into 50 ml flask and 20 ml toluene (Analar grade) added. After shaking for 30 min the liquid phase of the extract was measured spectrophotometrically at 420 nm using Jenway 6100 spectrophotometer. The THC in soil was estimated with reference to standard curve derived from fresh spent oil diluted with toluene. 6. Data analysis Analysis of variance was performed using General Linear Model (GLM) procedure of MINITAB Software Release 13 (2000). Experimental precision achieved was reported by standard error (SE) at P < 0.05 level. 4. Sampling 7. Results Soil samples were collected at 0–20 cm depth from each plot at 3, 6 and 12 months each year after application of treatments for metal concentrations, while samples were collected at same depth at the end of 2 years for residual oil content determination. These samples were air-dried at room temperature and pre-sieved using 2 mm sieve for the analyses. 7.1. Distribution of heavy metals relative to treatments applied Results presented in Figs. 1 and 2 shows Cr, Ni, Pb and Zn levels in treated and untreated plots relative to the sampling periods. Quality control of the Aqua Regia extraction Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS 4 J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx a 90 80 70 Conc. (mg/kg) 60 Cr Ni Pb Zn 50 40 30 20 10 +5 % SP +5 % SP PW PM 5% SP +5 % SP D C 2. 5% SP +2 .5 % SP PM +2 .5 % PW SP +2 .5 % SP CD 0. 5% SP +0 .5 % SP PM +0 .5 % PW SP +0 .5 % SP C D PM PW C CD 0 Treatments b 160 140 Conc. (mg/kg) 120 100 Cr Ni Pb Zn 80 60 40 20 5% SP D+ 5% SP PM +5 % PW SP +5 % SP C 2. 5% SP +2 .5 % S PM P +2 .5 % PW SP +2 .5 % SP D C 0. 5% SP +0 .5 % SP PM +0 .5 % PW SP +0 .5 % SP C D PW D C PM C 0 Treatments C 100 90 80 Conc. (mg/kg) 70 60 50 Cr Ni Pb Zn 40 30 20 10 +5 % SP SP PW % SP PM +5 % SP 5% +5 CD +2 .5 % SP +2 .5 % PW SP +2 .5 % SP PM SP 2. 5% D C 0. 5% SP D+ 0. 5% PM SP +0 .5 % PW SP +0 .5 % SP C PW PM C D C 0 Treatments Fig. 1. Spent oil-induced heavy metal concentrations (mg/kg) during 1st year pollution. (a) 3 months; (b) 6 months; (c) 12 months. Vertical bars represent the SE. Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx 5 Fig. 2. Spent oil-induced heavy metal concentrations (mg/kg) during 2nd year of pollution. (a) 3 months; (b) 6 months; (c) 12 months. Vertical bars represent the SE. method used for determination of the metal concentrations was done with the aid of reference soil sample from the International Atomic Energy Agency (IAEA). Heavy metal values from the reference soil sample were compared with the IAEA Certified Reference Values supplied by IAEA with the sample. The quality control check showed that Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS 6 J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx the Aqua Regia extraction method accounted for more than 70% Cr, Ni, Pb and Zn concentrations in this experiment. The general trend in the 1st and 2nd year (Figs. 1 and 2) indicated that there were significant (p < 0.05) accumulation of Cr, Ni, Pb and Zn in soils polluted with spent oil and plots supplemented with organic wastes than the control. This study further showed higher accumulation of Cr and Zn (Figs. 1 and 2), relative to other metals, with spent oil pollution. However, addition of organic wastes to the oil polluted soils significantly (p < 0.05) led to reduction in the levels of these metals. The distribution of each metal in the 1st year showed that Cr levels ranged between 6.6 mg/kg (control) and 78.3 mg/kg (5%SP) at 3 months, 7.0 mg/kg (control) and 124.1 mg/kg for plots treated with PW + 0.5%SP at 6 months and 7.0 mg/kg (control) and 89.1 mg/kg (5%SP) at 12 months. Ni concentration was least in the control plot (0.04 mg/kg, while the highest concentration (3.25 mg/kg) observed in plots treated with only 5%SP for 3 months was significantly (p < 0.05) different from the control. At 6 months, the highest Ni accumulation (3.52 mg/kg) was observed in plots treated with PW + 2.5%SP, whereas plots treated with only 5%SP had highest concentration (3.56 mg/kg) at 12 months (Fig. 1). Distributions of Pb and Zn in the first year (Fig. 1) for plots polluted with spent oil and spent oil polluted plots supplemented with organic wastes show significant increase (p < 0.05) in these metal concentrations with increase in oil pollution levels. The overall sequence of Cr, Ni, Pb and Zn accumulation in plots polluted with oil, was 3 months > 6 months > 12 months indicating reduction in the levels of these metals with time (Fig. 1), irrespective of pollution levels. The only exceptions observe were in the plots polluted with 5%SP where levels of Cr increased to 90.6 mg/kg and 89.1 mg/ kg for 6 months and 12 months, respectively when compared with 78.3 mg/kg for 3 months. However, in oil polluted plots amended with organic wastes, i.e. CD, PM and PW, Cr levels were higher in the 6 months compared with 3 and 12 months; while the general sequence for Ni, Pb and Zn was 3 months > 6 months > 12 months. Since there is currently no legislative values for land contamination by metals for Nigeria, the tolerable levels of Kabata-Pendias and Pendias (1984) commonly used for evaluation of soils around the world was adopted for this study. According to Kabata-Pendias and Pendias (1984), corresponding values for Cr, Ni, Pb and Zn are 75, 100, 100 and 70 mg/kg, respectively. Values above these tolerable levels are considered phytotoxically excessive (Kim et al., 2002).The values observed at 3 months (Fig. 1) for Cr, Ni, Pb and Zn were generally below these limits. Cr concentration of 78.3 mg/kg for plots treated with only 5%SP was above the tolerable limit at 3 months. At 6 months in the first year, Cr levels in CD + 0.5%SP (116.4 mg/kg), PM + 0.5%SP (86.9 mg/kg), PW + 0.5%SP (124.1 mg/kg), 2.5%SP (84.7 mg/kg), CD + 2.5%SP (82.7 mg/kg), PW + 2.5%SP (84.04 mg/kg), 5%SP (90.6 mg/kg), CD + 5%SP (113.1 mg/kg) and PW + 5%SP (87.5 mg/kg)) were above the 75 mg/kg tolerable limit of Kabata-Pendias and Pendias (1984). However, Ni, Pb and Zn concentrations at this sampling period were below their tolerable limits. Generally, application of organic wastes to oil polluted plots at 6 months show elevated accumulation of Cr in plots supplemented with cow dung (CD) and pig waste (PW), particularly at 2.5% and 5% oil pollution levels. However, PM led to reduction in Cr released into the soil when compared with plots polluted with only spent oil (Fig. 1). Observation at 12 months (Fig. 1) indicated increase in Ni concentrations in all the treated plots, and reduction in Cr, Pb and Zn levels when compared with observations at 6 months. Whereas, only Cr concentration of 89.1 mg/ kg for 5%SP treated plots was above the tolerable limit. Heavy metals accumulation in the 2nd year of this study (Fig. 2) following repeat application of treatments generally followed the trend observed in the first year, indicating that treatment with only oil and oil-polluted plots supplemented with organic wastes led to elevated metal concentrations, particularly Cr. The metal values were significantly (p < 0.05) higher in treated plots than the control (Fig. 2). Cr levels at 3 months (Fig. 2) were 67.8 mg/kg for 0.5%SP, 68.0 mg/kg for 2.5%SP and 75.9 mg/kg for 5%SP. The concentration of Cr (75.9 mg/kg) observed in plots treated with only 5%SP was significant (p < 0.05) different than values observe for 0.5%SP and 2.5%SP treatments. The general trend for Ni, Pb and Zn concentrations at 3 months, for both plots treated with only spent oil and oil-polluted soils amended with organic wastes, was 5%SP > 2.5%SP > 0.5%SP representing increase in metals levels with increase in oil pollution. Overall observations with time of sampling in the 2nd year (Fig. 2) followed the order 12 months > 3 months > 6 months for Cr and Ni and 3 months > 6 months > 12 months for Pb and Zn. These trends indicate higher accumulation of Cr and Ni in the 12th month, while Pb and Zn levels decreased with time of sampling. Zn levels, relative to other metals, were higher in the 2nd year following re-application of treatments than values observe in the 1st year. Metal levels in the 2nd year were generally lower than the tolerable limits considered to be phytotoxic. The only exceptions were Cr levels of 75.9 mg/kg for 5%SP (3 months), 75.6 mg/kg and 84.3 mg/kg for 2.5%SP and 5%SP, respectively in 12 months which were above the tolerable limits. This study show elevated accumulation of metals with spent oil pollution following the order 5%SP > 2.5%SP > 0.5%SP. The organic wastes (CD, PM and PW) were applied to minimize the negative effects of this oil, which is normally disposed off indiscriminately in Nigeria, into the environment. The choice of these animal wastes was because they are abundantly available in Nigeria, and a cheaper remediation option than the expensive chemi- Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx cal and physical methods. Observations show that these organic wastes led to significant (p < 0.05) reduction in the level of these metals when compared with plots treated with only oil. However, the effectiveness of these wastes in ameliorating the negative effect of the oil-induced metals was PM > PW > CD, indicating that poultry manure (PM) followed by pig waste (PW) were better for immobilizing these metals within the soil. Sequestration of metals within the soil matrix normally reduces their release into the solution phase of soil which could ultimately contaminate or pollute surface and ground waters. 7.2. Degradation of the spent oil as mediated by the organic wastes The extent of degradation of total hydrocarbon content (THC) at the end of two years of spent oil pollution mediated by the organic waste supplements is presented in Table 2. The THC or whole products analytical method, instead of analysis of individual hydrocarbon fractions, was adopted for this study because spent or used lubricating oil is highly variable (Tauscher, 1988), and have altered structure due to combustion process. At the end of 2 years of oil pollution, CD + 0.5%SP had the highest THC reduction of 88.1% (8814 mg/kg), while PM + 2.5%SP had 83.6% (41,789 mg/kg) reduction for plots with 50 g/kg total oil loading (Table 2). However, the influence of these organic wastes in stimulating biodegradation of this waste-lubricating oil in soils that received 100 g/kg total oil loading showed PM + 5%SP having highest THC reduction of 74,767 mg/kg, representing 74.8% decrease in THC when compared with plots treated with only 5%SP. The effectiveness of the organic wastes in stimulating biodegradation of the oil, as evaluated by the net loss corTable 2 Gravimetric loss of total hydrocarbon content (THC) after 2 years of spent oil pollution Treatments Spent oil loading (mg/kg) Residual THC (mg/kg); n = 4 Total % loss in THC Net % loss due to organic wastes 0.5%SP CD + 0.5%SP PM + 0.5%SP PW + 0.5%SP 2.5%SP CD + 2.5%SP PM + 2.5%SP PW + 2.5%SP 5%SP CD + 5%SP PM + 5%SP PW + 5%SP 10,000 10,000 10,000 10,000 50,000 50,000 50,000 50,000 100,000 100,000 100,000 100,000 2454 1186 1957 1215 14,550 12,984 8211 8539 29,071 28,405 25,233 25,432 75.5 88.1 80.4 84.9 70.9 74.0 83.6 82.9 70.9 71.6 74.8 74.6 NA 12.6 4.9 9.4 NA 3.1 12.7 12.0 NA 0.7 3.9 3.7 Total % loss = [{Spent oil loading – residual THC (treatment)}/spent oil loading] · 100. Net % loss = % loss in THC (treatment) – % loss in spent oil only. NA = not applicable. SP = spent oil; CD = cow dung; PM = poultry manure; PW = pig waste. 7 responding to each organic waste, indicated that cow dung (CD) made the highest reduction (12.6%) in THC for 0.5%SP treatment (Table 2); whereas poultry manure (PM) was more effective at 2.5% and 5% oil concentrations. Overall observation indicated that PM was a better nutrient supplement in stimulating microbial degradation of this spent oil. 8. Discussion 8.1. Heavy metals and hydrocarbon contents relative to treatment applied The increase in heavy metal concentrations via spent oil and organic wastes additions relative to the control was similar to the observations of Muniz et al. (2004), Adeniyi and Afolabi (2002), Davies (1997), Adeniyi (1996) and Markus and McBratney (1996). For example, Adeniyi and Afolabi (2002) reported elevated total petroleum hydrocarbons (TPH) and heavy metals contamination around locations of refined petroleum products handling facilities in Lagos metropolis (Nigeria). Findings reported in this study and by these workers confirmed observation of Albers (1995) who reported that heavy metals were found associated with petroleum. Also, Whisman et al. (1974) observed that most heavy metals such as Va, Pb, Al, Ni and Fe that were below detection in unused lubricating oil gave high concentrations in used oil. The observed decrease in metal concentrations with additions of organic wastes could be attributed to the ability of these amendments to immobilized contaminants in soil. For example, Arias et al. (2002) found humic acid, a component of soil organic matter, to enhance the metal adsorption capacity of mineral surfaces, and in particular kaolin. Also, Ye et al. (1999) observed that lime and pig manure resulted in reduction of electrical conductivity, DTPA-extractable concentrations of Zn, Pb and Cd in Pb/Zn mine tailings. It should be noted that the observed increase in metal levels in oil polluted soil supplemented with organic wastes, relative to plots amended with only organic wastes, could be attributed to increase mineralization of spent oil with addition of these organic wastes, thereby leading to release of basic components of the oil. Since heavy metals were observed to be associated with petroleum products, biodegradation of the spent oil mediated by addition of CD, PM and PW, even though led to decrease in the total hydrocarbon content, impacted negatively on the environment with the observed elevated release of metals. Since oil degradation is a natural process limited by temperature, pH and scarcity of nutrients such as N and P (Ladousse and Tramier, 1991; Leahy and Colwell, 1990), the higher rate of THC reduction observed in this study with addition of poultry manure (PM) could be due to its higher N and P contents, required for microbial growth and activity, shown in Table 1 when compared with cow Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS 8 J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx dung (CD) and pig waste (PW). It must be noted that the observed reduction in spent oil or THC may not only be due to the biodegradation process induced by nutrient addition, but other processes such as volatilization, adsorption to organic compounds and other abiotic factors are equally implicated in the reduction process. Metal concentrations observed in this study might be considered low after 2 years, when compared with the tolerable limits of Kabata-Pendias and Pendias (1984). Not withstanding this, concentrations of metals observed in this study still posed a potential risk. In fact people are moving away from using threshold values because of some fundamental problems associated with this approach. Some of these problems according to DEFRA (2002) are: (i) difficulties in establishing concentrations of contaminants beyond which risks from exposure to these contaminants would be ‘‘unacceptable’’; (ii) values that are applicable across a range of soil types and site conditions; (iii) incomplete information on contaminant behaviour, human activity patterns and contaminant toxicology and (iv) various countries have set different quantitative criteria that reflects the particular environmental and legal conditions that exist in those countries, so that simple comparisons of quantitative criteria used in different countries can be misleading. All these factors make it difficult to derive generally applicable criteria. Data presented in Table 1 indicated that the waste-lubricating oil contains Pb (240 mg/kg) and Zn (486 mg/kg) at concentrations that are very toxic when compared with Cr (6.5 mg/kg) and Ni (3.07 mg/kg). The low concentrations of Pb and Zn thereafter observed following application of this waste (Figs. 1 and 2), relative to Cr, could also be attributed to preferential uptake of Pb and Zn than Cr by plants. Alloway (1990) reported Pb and Zn as some of the metals which are readily absorbed by plants. While it has generally been assumed that these metals are immobile in managed agricultural soils (McBride, 1995), some factors that enhance their mobility include the properties of the metals, soil texture, pH and competing cations in the soil solution (Udom et al., 2004). Investigations by some workers on heavy metals in soils tend to show that metals release to the soil in waste accumulate on or very near to the surface layers of the soil (McBride, 1995). Dowdy and Volk (1984), in an extensive review of heavy metal movement in sewage sludge-treated soils, concluded that movement most likely occurred where heavy disposal of sewage sludge was made on sandy, acidic and low organic matter (OM) soils, receiving high rainfall or irrigation, an environment almost similar to the alfisol studied. Since organic carbon (OC) contents of the studied site (8.3 g/kg), spent oil (30.7 g/kg) and those of the organic supplements (CD, PM and PW) are high (Table 1), OM was suspected to be the main factor determining the fate of these metals in the waste-oil because of metal-organic complexation. In fact, McBride (1995) reported that metal-organic complexes have helped to decrease heavy metal mobility in soils. The reason for the differences in metal adsorption by the organic wastes, which followed the order PM > PW > CD, is not well understood. Ng et al. (2002) reported similar observation on the adsorption of geosium by activated carbon under laboratory conditions using Freundlich isotherm model. They concluded that the differences in geosium adsorption from carbon to carbon was complex and not well understood, and a number of carbon physical and chemical properties affect adsorption towards particular adsorbates. Further more, the slow release of Pb in the waste-oil into the soil agrees with the observation of van Erp and van Lune (1991) that Pb is bound as strongly to OM and would be released slowly over time, whereas Zn are not bound strongly to OM. Therefore, this slow release of Pb and Zn in the spent (waste) oil constitutes potential danger because of high OM content of this waste. In the light of the above reasons, concentrations of metals observed in this study are high enough to cause public concerns since most of these metals are not all required even in small amounts by living organisms (Tchernitchin et al., 1998; Martinez-Tabche et al., 1997; Freedman, 1996; Koomen et al., 1990). Therefore, the observed metal contents could constitute potential health and phytotoxic problems. Heavy metals could constitutes potential health problems because of many diseases such as anemia, nervous system disorders and depressed immune systems, asthmas, cancer, foetotoxic, etc. Those of phytotoxic problem could originate from the fact that some metals, such as Zn and Pb, are readily absorbed by plant roots and translocated to shoots. The plants then suffers severe yield reductions before humans, livestock or wildlife are at any risk from chronic life-time consumption of the crops (Chaney, 1994). 9. Conclusion This study was carried out to evaluate the effectiveness of cow dung, poultry manure and pig waste, which are abundantly available in Nigeria and cheaper, as remediation alternative to the expensive chemical and physical methods of oil pollution control. The study confirmed the association between heavy metals and waste-lubricating oil (spent oil) from petroleum. The distribution of the metals relative to treatments applied in the 1st and 2nd year of this study indicated significant (p < 0.05) accumulation of Cr, Ni, Pb and Zn in soil polluted with spent oil and plots supplemented with organic wastes. The study further showed higher concentration of Cr followed by Zn, relative to other metals, with waste-lubricating (spent oil) pollution; and this followed the order 5%SP > 2.5%SP > 0.5%SP indicating increase in metal levels with increase in oil dosage. However, addition of organic wastes to the oil polluted soil significantly (p < 0.05) led to reduction in the levels of the metals and total hydrocarbon. The effectiveness of the organic wastes in ameliorating the negative effects of the contaminant was PM > PW > CD indicating that poultry manure followed by pig wastes were better nutrients supplement for immobilization of these metals within the soil and in stimulating microbial Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx degradation of this waste oil. General distribution was 3 months > 6 months > 12 months, showing reduction with time of sampling. Since Cr was the main problem based on this study, this contaminant has the potential of being carcinogenic while Cr has been shown to have mutagenic potential. Therefore, this waste which is usually disposed off indiscriminately in Nigeria should be a major environmental concern to the regulatory agencies in terms of surface and underground water pollution and food-chain related problems. Acknowledgements The authors wish to acknowledge Prof. D.A. Davidson and Helen Ewen for the technical support provided J.K.A (the 1st author) when he was on research stay at the University of Stirling, Stirling, UK; and useful comments by the reviewers. References Adeniyi, A.A., 1996. Determination of cadmium, copper, iron, lead, manganese and zinc in water leaf (Talinum triangulare) in dumpsites. Environ. Int. 22, 259–262. Adeniyi, A.A., Afolabi, J.A., 2002. Determination of total hydrocarbons and heavy metals in soils within the vicinity of facilities handling refined petroleum products in Lagos Metropolis. Environ. Int. 28, 79– 82. Al-Ashen, S., Banat, F., Mohal, F., 1999. Sorption of copper and nickel by spent animal bones. Chemosphere 39, 2087–2096. Albers, P.H., 1995. Petroleum and individual polycyclic aromatic hydrocarbons. In: Haffman, D.T., Rattner, B.A., Burton, G.A., Cairns, J. (Eds.), Handbook of Ecotoxicology. Lewis, London, pp. 330–355. Alloway, B.J., 1990. Heavy Metals in Soil. John Wiley & Sons, New York, pp. 29–39. Anoliefo, G.O., Vwioko, D.E., 1995. Effect of spent lubricating oil on the growth of Capsicum annum L and Lycopersicon esculentum Mill. Environ. Pollut. 99, 361–364. Anon, 1985. Collection and disposal of oily wastes in Nigeria. Report prepared by RRI (Nig.) Ltd., for the Petroleum Oil Wastes Disposal Committee, 22 April 1985. Arias, M., Barral, M.T., Mejuto, J.C., 2002. Enhancement of copper and cadmium adsorption on kaolin by the presence of humic acids. Chemosphere 48, 1081–1088. Brady, N.C., Weil, R.R., 2002. The Nature and Properties of Soils. Pearson Education, New Jersey, pp. 797–837. Chaney, R.L., 1994. Trace metal movement in soil-plant systems and bioavailability of biosolids. In: Capp, C.E., Larson, W.E. (Eds.), Sewage Sludge Land Utilization and the Environment. Soil Sci. Soc. Ame. Publ., Madison WI, pp. 27–31. Davies, B.E., 1997. Heavy metal contaminated soils in an old industrial area of Wales, Great Britain: source identification through statistical data interpretation. Water Air Soil Pollut. 94, 85–98. DEFRA (Department for Environment, Food and Rural Affairs and the Environment Agency), 2002. Assessment of risks to human health from land contamination: An overview of the development of soil guideline values and related research’. Environment Agency: Rio House, Bristol. Dowdy, R.H., Volk, V.V., 1984. Movement of heavy metals in soils. In: Nelson, D.W., Elrick, D.E., Tanji, K. (Eds.), Chelate, mobility and reactivity in soil systems. Soil Sci. Soc. Ame. Publ., Madison WI, pp. 229–240. 9 Edebiri, R.A.O., Nwanokwale, E., 1981. Control of pollution from internal combustion engine used lubricant. In: Proceedings International Seminar on Petroleum Industry and the Nigerian Environment, pp. 9–12. Environment Canada, 1996. The state of Canada’s environment. Ottawa: Public Works and Government Services Canada. FDALR (Federal Department of Agricultural Land resources), 1990. Soil Map of Nigeria Project: Soil of Ogun-State 148, pp. 63–65. Freedman, B., 1996. Environmental Ecology: The Impacts of Pollution and Other Stresses on Ecosystem Structure and Function. Academic Press, New York, pp. 54–62. Huang, Y.F., Huang, G.H., Wang, Q.G., Lin, Q.G., Chakwa, A., 2006. An integrated numerical and physical modeling system for an enhanced in situ bioremediation process. Environ Pollut. 144, 872– 885. Kabata-Pendias, A., Pendias, H., 1984. Trace Elements in Soil and Plants. CRC Press, Boca, Raton, pp. 323. Keay, R.W., 1959. Derived Savannah: Derived from what? Bulletin D. I. F. A. N. Series A 21, 427–438. Kim, Ju-Yong, Kim, Kyoung-woong, Lee, Jong-Un, Lee, Jin-Soo, 2002. Assessment of As and heavy metal contamination in the vicinity of Duckum Au–Ag mine, Korea. Environ. Geochem. Health 24, 215– 227. Koomen, I., McGrath, S.P., Giller, K.E., 1990. Mycorrhizal infection of white clover is delayed in soils contaminated with heavy metals from past sewage sludge applications. Soil Biol. Biochem. 22, 871– 873. Ladousse, A., Tramier, B., 1991. Results of 12 years of research in spilled oil bioremediation. Inipole EAP 22. In: Proceedings of 1991 Oil Spill Conference. American Petroleum Institute, Washington, DC. Leahy, J.G., Colwell, R.R., 1990. Microbial degradation of hydrocarbons in the environment. Microbiol. Rev. 54, 305–315. Markus, J.A., McBratney, A.B., 1996. An urban soil quality: heavy metals in Glebe, Australia. Aust. J. Soil Res. 34, 453–465. Martinez-Tabche, L., Mora, B.R., Faz, C.G., Castelan, I.G., Ortiz, M.M., Gonazlez, V.U., Flore, M.O., 1997. Toxic effect of sodium dodecylbenzene-sulfonate, lead, petroleum and their mixtures on the activity of acetylcholinesterase of Moina macrocopa in vitro. Environ. Toxicol. Water Qual. 12, 211–215. McBride, M.B., 1995. Toxic metal accumulation from agricultural use of sewage sludge. Are USEPA regulations protective? J. Environ. Qual. 24, 5–18. Minitab Statistical Software Release 13.1, 2000. Minitab Inc., USA. Mohan, D., Singh, K.P., 2002. Single- and multi-component adsorption of cadmium and zinc using activated carbon derived from bagasse- an agricultural waste. Water Res. 36, 2304–2318. Muniz, P., Danulat, E., Yannicelli, B., Garcia-Alonso, J., Medina, G., Bı́cego, M.C., 2004. Assessment of contamination by heavy metals and petroleum hydrocarbons in sediments of Montevideo Harbour (Uruguay). Environ. Int. 29, 1019–1028. Ng, C., Losso, J.N., Marshall, E.W., Rao, R.M., 2002. Freundlich adsorption isotherms of agricultural by-product-based powder activated carbons in geosmin-water system. Biores. Technol. 85, 131– 135. Ryan, J.A., Zhang, P., Chou, J., Sayers, D.E., 2001. Formation of chloropyromorphite in a lead-contaminated soil amended with hydroxyapatite. Environ. Pollut. 50, 493–500. Salt, C., 1998. Heavy metals in sewage farm ecosystem. Schriftreihe des Fachbereichs der Landshsftsentwicklung der Teknische Unisersitaet, Berlin Nr. 53, pp. 214. Tauscher, W., 1988. The option for recycling and re-utilizing used petroleum oils. Nat. Res. Dev. 28, 100–107. Tchernitchin, N.N., Villagra, A., TChernitchin, A.N., 1998. Antiestrogenic activity of lead. Environ. Toxicol. Water Qual. 13, 43–53. Udom, B.E., Mbagwu, J.S.C., Adesodun, J.K., Agbim, N.N., 2004. Distribution of zinc, copper, cadmium and lead in a tropical ultisol after long-term disposal of sewage sludge. Environ. Int. 30, 468– 470. Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048 ARTICLE IN PRESS 10 J.K. Adesodun, J.S.C. Mbagwu / Bioresource Technology xxx (2007) xxx–xxx van Erp, P.J., van Lune, P., 1991. Long-term heavy metal leaching from soils, sewage sludge and soil/sewage mixtures. Environ. Sci. Toxicol. 25, 701–711. Whisman, M.L., Goetzinger, J.W., Cotton, F.O., 1974. Waste lubricating oil research. In: An Investigation of Services Re-refining Methods. Bureau of Mine, Bartlesville, Energy Research Center. Ye, Z.H., Wong, J.W.C., Wong, M.H., Lan, C.Y., Baker, A.J.M., 1999. Lime and pig manures as ameliorants for revegetating lead/zinc mine tailings: a greenhouse study. Biores. Technol. 69, 35–43. Zhu, Y.G., Chen, S.B., Yang, J.C., 2004. Effects of soil amendments on lead uptake by two vegetable crops from a lead-contaminated soil from Anhui, China. Environ. Int. 30, 351–356. Please cite this article in press as: Adesodun, J.K., Mbagwu, J.S.C., Distribution of heavy metals and hydrocarbon contents in ..., Bioresour. Technol. (2007), doi:10.1016/j.biortech.2007.05.048