Jul 4, 2013 - The ECWA secondary school football field was used as the control site for the ... collected about 100m away from the mechanic site where there are .... level observed is far below that reported in Imo, South â East Nigeria 20.
May 2013- July 2013, Vol. 3, No. 3; 2337-2347.
E- ISSN: 2249 –1929
Journal of Chemical, Biological and Physical Sciences An International Peer Review E-3 Journal of Sciences
Available online at www.jcbsc.org Environmental Sciences Research article
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Contributions of Automobile Mechanic Sites to Heavy Metals in Soil: A Case Study of North Bank Mechanic Village Makurdi, Benue State, Central Nigeria Aloysius A. Pam *, Rufus Sha’Ato 1 and John O.Offem2 *Department of Chemistry, Federal University Lokoja, P.M.B1154, Lokoja, Nigeria. 1
Department of chemistry,University of Agriculture, P.M.B 2373, Makurdi, Benue State,Nigeria. 2
University of Calabar, Calabar, Crose River State, Nigeria.
Received: 5 June 2013; Revised: 4 July 2013; Accepted: 18 July 2013
Abstract: The distribution of six heavy metals (Pb, Cu, Zn, Mn, Ni and Cd) in soil around North Bank automobile mechanic site in Benue State, North Central Nigeria were studied using AAS. Results of the analysis revealed that majority of heavy metal concentrations (mgkg-1 ) of the samples were above background levels and threshold limits recommended for soils in some countries. The results indicate the following levels Cu, (24.6mgkg-1), Pb (123 mgkg-1), Zn (42.7 mgkg-1), Mn (92.0mgkg-1), Ni (8.44mgkg-1) and Cd (0.60 mgkg-1) with a distribution pattern in the order: Pb>Mn>Zn>Cu>Ni>Cd. Factors which influence the mobility of metals in soils were determined such as pH, cation exchange capacity, organic matter, moisture content and soil texture. Geoaccumulation index values of the metals in soils under study showed that the environment is highly polluted with Pb and Cu, and to a lesser degree with Ni. Both Cd and Mn showed moderate pollution status while the soil remains unpolluted with Zn. Key words: Geo accumulation index, soil, Heavy metals
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INTRODUCTION Pollution is a serious problem the world over in which thousands of millions of world inhabitants suffer health problem related to waste generated from anthropogenic activities. Soil being one of the repositories for anthropogenic waste1, Biochemical processes can mobilize the chemical substances contained in it to pollute water supplies and impact food chains1 thereby causing great harm to man. The high toxic and persistent nature of heavy metals in the environment have made them priority pollutants 2.The unchecked industrial and human activities have contributed to toxic trace metals levels in surface and subsurface soils when compare to those contributed from geogenic process3.Anthropogenic metal emission into the atmosphere such as Pb, Hg, Zn, Cd and Cu are by 1 to 3 order of magnitude higher than natural influx4. Heavy metal is a general collective term that applies to a group of metals and metalloids with an atomic density greater5 than 5g/cm3.Examples of heavy metals/metalloids include Mercury (Hg) ,Lead (Pd), Cadmium (Cd),Arsenic (As),Copper (Cu),Manganese (Mn) etc. According to Karen4, trace metal levels in soils can be indicators of the concentrations of other pollutants that potentially related. Heavy metals, unlike organic pollutants, are elements, which occur naturally in the Earth crust. They therefore found naturally in soils and rocks with a subsequent rage of natural concentration in soils, sediment, waters and organisms6.Heavy metals belong to a group of elements whose hydrogeochemical cycles have been greatly accelerated by man. Anthropogenic release has given rise to higher concentrations of these metals relative to the normal back ground levels. The impact of pollution in vicinity of overcrowded cities and towns and industrial effluents and automobile exhaust has reached a disturbing magnitude, arousing public awareness7. According to 8Adelewole and Uchegbu, one of the major sources of increase heavy metal concentration of the ecosystem in Nigeria is automobile mechanic activities. In Nigeria, soil pollution problems associated with heavy metals have been widely reported9-21. In Nigeria, automobile mechanic workshops are located or concentrated in areas known as “Mechanic Villages”. These are places officially designated for repairs and servicing of motor vehicles22.The sources and mechanism of release of heavy metals into the soil and ground water of Automobile mechanic sites include engine oil and lubricating oil, engine and gear box recycling, battery charging, welding and soldering, automobile body work and spray painting and combustion processes. Waste emanating from such activities includes spent lubricants hydraulic fluids, worn-out parts, packaging materials, metal scraps, used batteries, discarded cans and stripped oily sludge. The conceptual (hypothetical) model in Fig 1 provides an overview of the expected sources and waste generated into soil within the automobile mechanic sites. The soil-plant barrier limits transmission of many heavy metals through the soil-crop-animal food chain, with the exception of Cd, Zn, Mn, Mo, and Se. Cadmium which has lower affinity for metal-sorbing Phases(for example, oxides) has the greatest potential for transmission through the food chain in levels that present risk to consumers23-26 . Pb, Hg, Cu, As, also have adverse effect on human health. Therefore, it becomes imperative to assess whether the levels of heavy metals in North Bank mechanic site is sufficient to affect the health of the inhabitants of the study area.
MATERIALS AND METHOD All chemicals used were analytical grade reagent. Study area and description of sites: Benue State, is located in the Central region of Nigeria (coordinates: 7.200N 8.450E). The state has an estimated population of over 5, 181,642 people and a 2338 J. Chem. Bio. Phy. Sci. Sec. D; 2013, Vol.3, No.3; 2337-2347.
total land area of about 40,000km2 .The sampling station was established within the State (Fig.1) in Makurdi to represent the dominant sources of heavy metals from auto mechanic activities. Makurdi is the capital city of Benue State in Nigeria. The city is located along the Benue River bank on latitude 7.440N and longitude 8.320E situated in a valley 100m above sea level. As at the year, 2007 Makurdi had an estimated population of 500,791 people with a total land area of about 200km2. The population in the city unevenly distributed such that commercial, industrial and agriculture, recreational and administrative, auto-mechanic sites and residential areas are scattered all over the city and these are point sources of heavy metals 27. This site was chosen for investigation, being one of the major mechanic sites in Makurdi. It is located in North Bank area of the city. It is surrounded by residential houses and located North of ECWA Secondary School. The ECWA secondary school football field was used as the control site for the area.
Fig.1: Map of Benue State showing the study site, Makurdi (Source: Adamu and Nganje,2010)
Sample collection and sample treatment: Nine samples collected randomly from the automobile Mechanic site at a depth of 0.02m using stainless van-veen Grab. One sample as control was also collected about 100m away from the mechanic site where there are neither car repairs nor commercial activities carried out. The samples placed in labeled polythene bags and transported to the laboratory. All soil samples subsequently air-dried to constant weight to avoid microbial degradation 28. They were homogenized, made lump free and gently crushed repeatedly using a mortar and pestle, and passed through a 2-mm plastic sieve prior to analysis. Heavy metal analysis: One gram of the dried fine soil sample was weighed and transferred into an acid washed round bottom flask containing 10ml concentrated nitric acid. The mixture was slowly 2339 J. Chem. Bio. Phy. Sci. Sec. D; 2013, Vol.3, No.3; 2337-2347.
evaporated over a period of 1 hour on a hot plate. Each of the solid residue obtained was digested with a 3:1 concentrated HNO3 and HClO4 mixture for 10 minutes at room temperature before heating on a hot plate .The digested mixture was placed on a hot plate and heated intermittently to ensure a steady temperature of 150oC over 5 hours until the fumes of HClO4 were completely evaporated17. The mixture was allowed to cool at room temperature and then filtered, using Whatman No.1 filter paper into a 50ml volumetric flask and made up to mark with deionized water after rinsing the reacting vessels to recover any residual metal. The filtrate was then stored in pre-cleaned polyethylene storage bottles ready for analysis. Heavy metal concentrations were determined using an Atomic Absorption Spectrophotometer (UNICAM AA68100Model), at the National Research Institute for Chemical Technology (NARICT), Zaria. The settings and operational conditions of the instrument were in accordance with the manufacturer’s specifications. The instrument was calibrated with analytical grade standard metal solutions (1mg/dm3) in replicates. The empirical data generated were subjected to statistical analysis. RESULTS AND DISCUSSION Soil properties: Physicochemical characteristics of soil such as pH, Organic Matter (OM), Cation Exchange Capacity (CEC), moisture content, particle size distribution are known to influence the interactions and dynamics of metals within the soil matrix. The results of the physicochemical characteristics of the soils are presented in Table 2. This summarizes the data in terms of the mean values with their respective range and standard deviation. In this study, the mean values of soil pH in automobile mechanic site ranged from 5.02 in CaCl2 to 6.26 in H2O which suggest that the soil is moderately acidic.(Table.2) .The cation exchange capacity range between 4.19 to 7.11 meq/100g, the organic matter was in the rage of 2.40 to 4.19% while moisture content ranged between 1.90 to 9.60% Concentration of Metals: Many studies have shown that urban soils receive loads of contaminants that are usually greater than in the surrounding sub-urban or rural areas due to the higher tempo of anthropogenic activities of urban settlement29; this is confirmed by this study. It is important to know that there are no soil quality guidelines for heavy metals in soils in Nigeria30, 31 and hence comparisons were made with those of other countries32. The concentrations of the metals, however, were relatively low in nearby control areas with same geology as the mechanical site. Lead: The mean value of Pb in soil obtained in this study was 123mg/kg. This value is deemed to be higher than the control level of (2.32 mg/kg ). The value of Pb obtained in this study is lower than the 1162 mg/kg reported by Nwachukwu et al, 33 in auto-mechanic village in Owerri in South East Nigeria,501.58 mg/kg reported by Udousoro et al.13, in South – South Nigerian and those in industrial areas in North West Nigeria (151.5 – 540.4 mg/kg). Allowable limits of Pb concentrations vary widely with country 32. The level of Pb obtained in this study is above the acceptable limits for soils in Austria, Poland, and Great Britain but below that in Canada, Japan and Germany. It is possible that this level of Pb elevated by the amount of waste oil, presence of automobile emissions, and expired motor batteries indiscriminately dumped by battery chargers and auto mechanics around their shops. Copper: Copper was present in all the soil samples investigated. This value is higher than that at the control site (2.32mg/kg). There is low distribution of Cu in the mechanic site in the present study with mean value of 24.6mg/k. This is below the maximum allowable limits in Australia (100mg/kg), Canada (100mg/kg), Poland (100mg/kg), Japan (125 mg/kg), Great Britain (100 mg/kg) and Germany 2340 J. Chem. Bio. Phy. Sci. Sec. D; 2013, Vol.3, No.3; 2337-2347.
(50 mg/kg). Soil in this study exhibited higher levels of contamination than 7.21mg/kg and 0.99 – 23.72mg/kg reported by 34Akoto et al, 34 and 35Yahaya et al35. Zinc: The Zinc content in all the soils had a mean value of 42. 7mg/kg. This value is higher than that at the control and suggests that, there is anthropogenic contribution. Since no industry exists in the vicinities of this area, we may assume that the primary source of Zn are probably the attrition of motor vehicle tire rubber by poor road surfaces, and the lubrication oils in which Zn is found as part of many additives as Zincdithiophates 36. The concentration of Zn in this investigation are small compared with many other studies 33,37, although comparable to that in Cameroon, South east Korea and that in Yauri LGA, in Kebbi State, Nigeria 35Yahaya et al,35 . Acidic pH makes easier the solubilisation of Zn compounds 36. In the present work pH ranged from 5.0 – 6.26 indicating only moderate soil acidity. Therefore, the mobility of Zn in soil layers might be expected to be at low rate. This could have accounted for the low value of Zn obtained in the investigated soil compare to other works. The value of Zn obtained in this site conforms to the acceptable limits in soil. Manganese: Mn obtained from this recorded mean values of 92 mg/kg. Although the concentration found for Mn is above the control level, there is, at present, no soil quality criteria established for Mn 4 38 , . However, judging by other articles 4,38 and mean concentration available in this study, it would suggest that this level of Mn in the soil investigated does not appear to be extensive but still substantial and need to be monitored to prevent any further increase. Nickel: The concentration of Ni in the soil investigated showed a distribution mean of 8.44 mg/kg and a mean content of 5.8 mg/kg for the control site. The result is relatively higher than value of 0.033 mg/kg reported in Akoto et al,34 and below 11.5 mg/kg in Ipeaiyeda et al31, ND – 8.62mg/kg in Shinggu et al39, and 17.38 – 16.52 mg/kg in Iwegbue et al11, Although the result is within the range of 4.20 to 48.62 mg/kg reported by Luter et al40, in the same study area. The anthropogenic distribution of Ni in this location could be attributed to the disposal of spent automobile batteries from the nearby auto-battery charger and various paint wastes and pigments, which have contributed to the contamination of the soil 13. The value for Ni is below the approved maximum allowable limits for heavy metals in soils regulated by various countries 32, which suggest that, for now, there is little anthropogenic contribution. Cadmium: The mean concentration of Cd examined at this area of study is 0.60 mg/kg and ranged from 0.32 – 1.0 mg/kg. The concentration in this site is relatively low compare to criteria acceptable in most countries32 but higher than the control value of 0.18 mg/kg. This finding of elevated Cd concentration is consistent with that of Luter et al.40, which investigated heavy metals in soils of auto-mechanic shops and refuse dump-sites in Makurdi, Nigeria and reported a range of 0.6 – 3.5 mg/kg, incidentally, the lowest value they reported is the same as the one in this study. The mean Cd level observed is far below that reported in Imo, South – East Nigeria 20. Variation in metal concentration in the study area: In order to have a comparative idea about the levels of contamination, data from this work was compared with those from the control sampling point taken to be the unpolluted or background value. The background value of an element is the maximum level of the element in an environment beyond which the environment is said to be polluted by the element41.
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The average level of these metals in the soil, around the auto-mechanic site indicated that they are not derived from the natural geology of the area as evident from the low level of metals in control sample. The heavy metals showed a hierarchical variation in the order Cu > Pb > Zn > Mn > Ni > Cd. There are high levels of variation in the investigated soils with large standard deviations shown by Pb, Cu and Zn. Manganese and Ni had moderate variability while Cd displayed the least variability. Large variations imply great heterogeneity of metals in soils while low variations show more or less homogenous distribution of metals in the soil42 and this could be traced to different levels of pollution, caused by varying degree of automobile waste dumps. In order to assess the impact of toxic trace metals in soil, a methodology adopted wherein various indices such as (i) Index of geo-accumulation (ii) Quantification of anthropogenic Metal were computed 3.The index of geo-accumulation (I-geo) enables the assessments of contamination by comparing current and pre-industrial concentrations3. Igeo is computed using the following equation: Igeo = log2(Cn/1.5Bn) Where Cn is the concentration of the heavy metal in the enriched sample and Bn is the concentration of the metal in the unpolluted samples or control. The factor 1.5 is introduced to minimize the effect of the possible variations in the background or control values, which may be attributed to lithogenic variations in the soil 43. The degree of metal pollution assessed in terms of seven contamination classes in order of increasing numerical value of the index44 as shown in Table 1 Table- 1: Seven classes of geo accumulation index. Class 0 1 2 3 4 5 6
soil quality Unpolluted unpolluted to moderately polluted moderately polluted moderately polluted to highly polluted Highly polluted Highly polluted to very highly polluted Very highly polluted.
The proportion of anthropogenic metal was computed for each metal. The metal content of the control (background) samples were taken to represent the lithogenic metal. The equation used is as follows: Anthropogenic metal =
x – xc x 100 x Where x = average concentration of the metal in the soil, and xc = average concentration of the metal in the control samples 45. Geo-Accumulation Index (I-geo): Results from the calculation of Geo-accumulation index (I-geo) in soil are also presented in Table 4. The pollution status of the metals in the environment expressed in terms of the geo-accumulation indices showed that the environment is highly polluted with Pb and Cu, and to a lesser degree with Ni. Both Cd and Mn showed moderate pollution status. The negative values of Zn are an indication that the soil is not polluted by Zn.
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Quantification of soil contamination: Quantification of the anthropogenic input of heavy metals in soil is as presented in Table 4.The quantification of heavy metals obtained for the Mechanic site is presented below: Pb > Cu > Cd > Mn > Ni> Zn I-geo factor is not readily comparable with EF due to the nature of I-geo calculation which involves a logarithm function and a back ground multiplication43 factor 1.5 . The anthropogenic inputs in soils of the investigated mechanic site generally decreased in the order; Cu > Pb > Ni > Cd > Mn > Zn. There is anthropogenic inpute in soil of the study area.This is an indication that these metals are derived from the waste generated from this machanic site. The Degree of anthropogenic pollution is high for Pb(95.9%), Cu(90.6%), Cd(70%) and Mn(58.1%), moderate for Ni(49.8%) and low for Zn(1.98%).
Pb, Cu, Zn, Ni, etc -lubricating oil -accidental spills -Transmission fluids
-spent lubricants -spent hydraulic fluids -stripped oily sludge
-Welding and soldering -chassis body works -spray – painting -combustion processes
Engine and gear box recycling
Packaging materials and discarded cans
-Aerosols -metal scraps -Machinery wear/tear -Worn-out parts
Recharging of carbatteries
-Used batteries -Acid from charging
-Underground water -Micro organisms -Plants
Soil contamination (effect) Environmental impact
-Acidification of soil -Phyto-toxicity -Reduce survival growth of micro organism and earth worms. -Bio-magnify up the food chain
-Contamination of ground water.
Fig.2: A Conceptual model for waste generation in automobile mechanics sites and the environmental impact.
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Table-2: Mean vales of pH, organic matter, cation exchange capacity, percentage, moisture content and particle size Distribution
Soil Properties pH (H20) pH (CaCl2) CEC OM Moisture Content Sand Silt Clay
North bank Mechanic Site Mean ±SD
6.26±0.12 5.45±0.24 6.05±0.87 3.06±0.37 5.46±2.03
6.12-6.52 5.20-60 4.19-711 2.40-4.19 1.90-9.60
80.76±6.01 8.02±2.15 3.19±0.67
70.30-89.52 5.0-10.30 2.5-4.60
Table- 3: Heavy metal concentrations in the soil expressed in range, mean and standard deviation. North bank Mechanic site Element Pb Cu Zn Mn Ni Cd
123.0±90.5 24.6±0.57 42.7±0.57 92.0±19.5 8.44±2.3 0.60±0.13
25.8-377.8 7.52-51.7 41.7-43.1 68.7-128.0 5.84=13.0 0.32-1.0
Table- 4: Geo- accumulation index (I-geo), quantification of contamination and background concentrations (BC) of heavy metals in soil of North bank mechanic site. Sample I-geo Quantification of Contamination (%) BC
Pb 4.0 95.9
Cu 2.74 90.6
Zn -0.56 1.98
Mn 0.67 58.1
Ni 0.33 47.5
Cd 1.12 70
CONCLUSION The assessment of the heavy metal levels in this study indicated that soil investigated is contaminated with most of these metals. Evidence of contamination of this soil by Pb, Cu, Zn, Mn, Ni and Cd were obvious when compared to the control site, with Pb and Mn presenting the highest concentrations as shown by the following order of aboundance Pb>Mn>Zn>Cu>Ni>Cd. This result at present is higher than an earlier one recorded from similar studies by Luter et al40, and is an indication that there is an ongoing build up of heavy metals at the Mechanic site studied and levels of some of the metals are 2344 J. Chem. Bio. Phy. Sci. Sec. D; 2013, Vol.3, No.3; 2337-2347.
already higher than permissible limits for several countries. The health implication of this trend is obvious and raises significant concern for safety of the environment. The sum of the contamination factors for all the metals examined indicate considerable degree of contamination in the soil and that the contamination is a consequence of human activities. In addition, the Government should put stricter environmental laws and regulations in place in order to curb this trend and all relevant authorities involved in the use of automobile mechanic sites, in Benue State, should be adequately informed of the impending danger associated with indiscriminate dump of waste containing heavy metals.
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Corresponding author: Aloysius A. Pam; Department of Chemistry, Federal University Lokoja, P.M.B1154, Lokoja, Nigeria.
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