Assessment of Heavy Metals in a Soil Contaminated by Petroleum Hydrocarbons at Ebudu, Rivers State, Nigeria.

By Nwadiogbu, JO; Ikelle, II; Onwuka, JC; Ikeh, OA; Nwankwo, NV; Anarado, IL (2024). Greener Journal of Environmental Management and Public Safety, 12(1): 10-15. Return to Issue Full text - PDF Full text - HTML Full text - EPUB Audio Version https://www.gjournals.org/wp-content/uploads/2024/04/031724033-Nwadiogbu-et-al.mp3 Or highlight the text below to listen. Greener Journal of Environment Management and Public Safety ISSN: 2354-2276 Vol. 12(1), pp. 10-15, 2024 Copyright ©2024, Creative Commons Attribution 4.0 International. https://gjournals.org/GJEMPS Article's title & authors Assessment of Heavy Metals in a Soil Contaminated by Petroleum Hydrocarbons at Ebudu, Rivers State, Nigeria. Nwadiogbu J.O. 1*, Ikelle I.I. 2, 3Onwuka J.C., 4Ikeh O.A., 4Nwankwo N.V and 4Anarado I.L Department of pure and industrial chemistry, Chukwuemeka Odumegwu Ojukwu University Uli, Anambra state, Nigeria. Department of Industrial chemistry, Ebonyi State University, Abakaliki, Ebonyi State, Nigeria. Department of Chemistry, federal university Lafia, Nassarawa state, Nigeria. Department of pure and industrial chemistry, Nnamdi Azikiwe University, Awka, Anambra state, Nigeria. ARTICLE INFO ABSTRACT Article No.: 031724033 Type: Research Full Text: PDF, PHP, HTML, EPUB, MP3 Surface (0–15 cm) and subsurface (15–30 cm) depth of soil samples contaminated with petroleum hydrocarbons were collected from impacted sites at Ebudu community in River State, Nigeria, after a field reconnaissance survey. An uncontaminated soil sample collected 500m from the impacted sites, but within the same geographical area, was used as a control. Trace heavy metals such as, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, and Zn which are normal constituents of petroleum hydrocarbon were determined by atomic absorption spectroscopy. Trace heavy metal concentrations ( mg kg− 1) were: As, 1.00 – 4.42 mg kg− 1; Cd, 1.76 – 7.50 mg kg− 1;Cr, 1.07 – 6.38 mg kg− 1;Cu, 1.84 – 9.78 mg kg− 1; Fe, 6.64 – 24.3 mg kg− 1; Hg 1.0– 4.18 mg kg− 1; Mn, 3.42 – 13.62 mg kg− 1;Ni, 2.02 –7.26 mg kg− 1; Pb, 4.57 – 22.3 mg kg− 1; and Zn, 3.38 – 21.71 mg kg− 1; in surface and subsurface soils. A positive correlation among the heavy metal contents shows pollution is from the same source (both oil pollution and allochthonous inputs). Fe, Mn, Pb and Zn were more enhanced (p<0.05) in the oil-spill-polluted soils, especially at surface depth, and this may be attributed to the fact that metal profiles in polluted soils penetrate a little below the 10-cm region, even after many years, thereby making the metal concentration in surface soils usually higher. Accepted: 18/03/2024 Published: 08/04/2024 *Corresponding Author Dr. Onyebuchi Nwadiogbu E-mail: onyebuchinwadiogbu@ yahoo.com Phone: +2348037573741 Keywords: Soil Pollution, Petroleum Hydrocarbon, Heavy Metal. INTRODUCTION Contamination of soil environment by hydrocarbons (mostly petroleum hydrocarbons) is becoming prevalent across the globe. This is probably due to heavy dependence on petroleum as a major source of energy throughout the world. The amount of natural crude oil seepage was estimated to be 600,000 metric tons per year with a range of uncertainty of 200,000 metric tons per year (1). Incidence of environmental pollution due to high rate of petroleum related activities in the Niger Delta area of southern Nigeria and other oil producing areas of the world has been associated with frequent oil spills, especially through oil wells blow outs, tanker accidents, bunkering, rupture of pipelines and sabotage. Disasters arising from such incidence results in the discharge of crude oil into the environment affecting both soil, air and water bodies. This threatens human health and that of the organisms that are dependent on the soil (2). Pollution of the soil with petroleum derivatives is often observed in municipal soils around industrial plants and in areas where petroleum and natural gas are obtained. Nigerian crude oil is known to have about 0.003 – 42.31 mg/kg of transition metals (V, Cr, Mn, Fe, Co, Ni and Cu) (15); some of which cannot be completely removed during the crude refining processes. Once they enter ecosystems, petroleum-based products initiate a series of processes, affecting both biotic and abiotic elements (12). Heavy metals contaminated soil from industrial waste; electronic wastes etc. on the other hand pose a serious threat to both man and animals in the environment if not properly remediated to the innocuous level. Environmental pollution by heavy metals which are released into the environment through various anthropogenic activities such as mining, energy and fuel production, electroplating, wastewater sludge treatment and agriculture is one of the world’s major environmental problem. Heavy metals or trace metals refer to a large group of trace elements which are both industrially and biologically important. Initially, heavy metals are naturally present in soils as natural components but as of now, the presence of heavy metals in the environment has accelerated due to human activities. This is a widespread problem around the world where excessive concentration of heavy metals such as Pb, Zn, Cr, Cu, Cd, Hg, and As can be found in soils (10). Soil contamination by heavy metals is consequently the most critical environmental problems as it poses significant impacts to the human health as well as the ecosystems. The contaminants are able to infiltrate deep into the layer of ground waters and pollute the groundwater as well as the surface water. Heavy metals in the soil subsequently enter the human food web through plants and they constitute risk to the ecosystem as they tend to bio-accumulate and can be transferred from one food chain to another. Heavy metals are discovered in various food chains where the results are usually detrimental to microorganisms, plants, animals and humans alike (10). The main threats to human health from heavy metals are related with exposure to lead, cadmium, mercury and arsenic (arsenic is a metalloid but is usually classified as a heavy metal). Heavy metals have been utilised by humans for thousands of years. Exposure to heavy metals continues although several adverse health effects of heavy metals have been known for a long time. For example, mercury is still used in gold mining in many parts of Latin America. Arsenic is still common in wood preservatives, and tetraethyl lead remains a common additive to petrol, although this use has decreased dramatically in the developed countries. Waste-derived fuels are especially prone to contain heavy metals which should be a central concern in the consideration for their use. Since the mid 19th century, production of heavy metals increased abruptly for more than 100 years, with associated emissions to the environment, particularly in less developed countries though emissions have lessened in most developed countries over the last century (10). Some heavy metals are dangerous to health or to the environment (e.g. mercury, cadmium, lead, chromium), some may cause corrosion (e.g. zinc, lead), some are harmful in other ways (e.g. arsenic may pollute catalysts). Some of these elements are actually necessary for humans in minute amounts (cobalt, copper, chromium, manganese, nickel) while others are carcinogenic or toxic, affecting, among others, the central nervous system (manganese, mercury, lead, arsenic), the kidneys or liver (mercury, lead, cadmium, copper) or skin, bones, or teeth (nickel, cadmium, copper, chromium). One of the largest problems associated with the persistence of heavy metals is the potential for bioaccumulation and biomagnification causing heavier exposure for some organisms than is present in the environment alone. Through precipitation of their compounds or by ion exchange into soils and muds, heavy metal pollutants can localize and lay dormant. Unlike organic pollutants, heavy metals do not decay and thus pose a different kind of challenge for remediation (10). The objective of this study was to examine the impact of oil spill on the heavy metal content of soil. MATERIAL AND METHOD Description of Study Area and Soil Sampling Soil samples were collected with a soil auger at surface depth (0-15cm) and subsurface depth (15 – 30cm) from five (5) petroleum hydrocarbon polluted sites (A, B, C, D, E) in Ebudu community, eleme Local Government Area of River State in southern Nigeria. The community is one of the communities crossed by oil pipelines in the Niger Delta area of Nigeria. A background sample or the control sample (F) was similarly collected 500m away from the oil pipeline area in the community, against the direction of drainage. Soil samples were air dried, crushed and passed through a 2 mm sieve. Samples were digested using 4-acid digestion method for total metal, in line with the USEPA (2007) 3050/305, as in EPA document SW-846. The SOLAAR UNICAM 969 atomic absorption spectrometer (AAS) was used for the metal analysis (5,19). Data were analyzed using descriptive statistics and Analysis of Variance (ANOVA). Test of significance of the means was by the Least Significant Difference (LSD). RESULT AND DISCUSSION The concentration of the different heavy metals determined in the six soil samples at different surface depths are given in Table 1a. All petroleum hydrocarbon contaminated soil samples were found to have reasonably higher concentration of the heavy metals than the values of the controlled soil sample collected some distance away from the site, with the concentrations of the elements within the regulatory limits as defined by U.S. EPA, 1993. The presence of metals in the uncontaminated soil indicates that heavy metals naturally occur in the environment and natural ecosystem (21). This further shows that they are natural components of the ecological system associated with one or more functions which may not be harmful at reduced concentrations but could become toxic at heightened doses. This finding is in harmony with prior reports of Hopkins (9). Heavy metal building in soils polluted with crude oil and its various products has been previously reported by Chen et al. (6), Agbogidi and Egbuchua (3), Chukwuma et al.(7), Tables 1a, 2a and 3a shows that Fe, Pb, Zn, Mn and Cu are more enhanced (P<0.05) in the oil - spill – polluted soils, especially at surface depth but below the regulatory limits defined by US EPA 1993. This may be attributed to the fact that metal profiles in polluted soils penetrate a little below the 10-cm region, even after many years, thereby making the metal concentration in surface soils usually higher (18). Nwachukwu et al., (7) similarly reported high values of Fe, Pb, Mn and Cu in an oil polluted soil. The high value of Fe may be attributed to the fact that most soils are Fe- rich in nature (17). Heavy metals have also been shown to affect the physical, chemical, biological and microbial properties of soils (7,14). Long term exposure may result in slowly progressing physical, muscular and neurological degenerative processes (13). The presence of these heavy metals in soils when absorbed by plants is capable of making plants potentially toxic and harmful to man as well as his livestock if ingested or consumed as food (3,20). As trace elements, some of the heavy metals like zinc, copper selenium are essential for the maintenance of body metabolism. At higher concentration, they can lead to poisoning. Lead, chromium, nickel are known to have serious consequences on the brain cells (8,11). Benson and Ebong (2005) noted that poor growth of crop plants in higher levels of oil treatment was primarily due to the toxic effect of heavy metals or mineral uptake. In Tables 1b, 2b and 3b, total contents of the heavy metals at different surface depths and irrespective of the surface depths, were significantly correlated, suggesting common origin of these elements in the soils (oil pollution and anthropogenic) (17). Table 1a: Heavy Metal Concentration (mg/kg) in Soil Samples at the Different Surface Depth Cu Mn Zn Fe Pb Cd Cr Ni Hg As A 0-15cm 9.6 12.24 19.08 23 21.05 6.2 5.98 7.23 4.18 4.42 15-30cm 5.32 9.61 11.84 14.25 13.09 3.09 3.06 4.42 1.82 2.32 B 0-15cm 8.8 13.2 20.02 24.3 22 7.5 6.01 6.4 4.12 4.08 15-30cm 4.96 9.84 11.98 15.26 12.23 4.08 4.48 3.89 2.26 2.2 C 0-15cm 9.2 14.43 18.04 21.6 20.01 6.24 5.24 6.18 3.11 4.02 15-30cm 4.84 8.92 10.82 12.63 11.92 3.67 3.76 4.52 1.88 2.26 D 0-15cm 9.78 13.62 21.71 22.3 22.3 7.02 6.38 7.26 3.37 3.35 15-30cm 4.84 8.45 12.38 14.33 11.58 3.73 3.35 4.28 1.97 1.97 E 0-15cm 4.57 6.63 7.43 9.3 7.48 3.08 3.12 4.16 2.23 1.83 15-30cm 2.68 3.42 4.72 6.64 4.81 1.87 1.07 2.05 1.07 1 F 0-15cm 3.89 6.53 6.36 9.28 6.98 3.66 3.31 3.92 1.98 1.98 15-30cm 1.84 3.64 3.38 6.86 4.57 1.76 1.08 2.02 1 1 Table 1b: Correlation of Heavy Metal Concentration Irrespective of the Surface Depth and Area Cu Mn Zn Fe Pb Cd Cr Ni Hg As Cu 1 Mn 0.4195 1 Zn 0.9724 0.4740 1 Fe 0.9661 0.5372 0.9859 1 Pb 0.9780 0.4999 0.9931 0.9921 1 Cd 0.9562 0.5901 0.9530 0.9600 0.9568 1 Cr 0.9455 0.4544 0.9478 0.9435 0.9425 0.9632 1 Ni 0.9778 0.3890 0.9527 0.9369 0.9538 0.9402 0.9595 1 Hg 0.9381 0.5764 0.9046 0.9323 0.9164 0.9497 0.9390 0.9376 1 As 0.9630 0.4973 0.9239 0.9575 0.9506 0.9375 0.9235 0.9455 0.9573 1 Table 2a: Heavy Metal Concentration (mg/kg) in Soil Samples at Surface Depth 0 – 15cm Cu Mn Zn Fe Pb Cd Cr Ni Hg As A 9.6 12.24 19.08 23 21.05 6.2 5.98 7.23 4.18 4.42 B 8.8 13.2 20.02 24.3 22 7.5 6.01 6.4 4.12 4.08 C 9.2 14.43 18.04 21.6 20.01 6.24 5.24 6.18 3.11 4.02 D 9.78 13.62 21.71 22.3 22.3 7.02 6.38 7.26 3.37 3.35 E 4.57 6.63 7.43 9.3 7.48 3.08 3.12 4.16 2.23 1.83 F 3.89 6.53 6.36 9.28 6.98 3.66 3.31 3.92 1.98 1.98 Table 2b: Correlation of Heavy Metal Concentrations at Surface Depth 0 – 15cm Cu Mn Zn Fe Pb Cd Cr Ni Hg As Cu 1 Mn 0.2767 1 Zn 0.9842 0.3939 1 Fe 0.9721 0.4770 0.9803 1 Pb 0.9861 0.4192 0.9958 0.9937 1 Cd 0.9240 0.5632 0.9681 0.9733 0.9735 1 Cr 0.9649 0.3997 0.9887 0.9721 0.9848 0.9675 1 Ni 0.9793 0.2400 0.9719 0.9470 0.9660 0.9018 0.9780 1 Hg 0.8724 0.5515 0.8826 0.9311 0.9031 0.8740 0.9021 0.8899 1 As 0.9211 0.4058 0.8896 0.9551 0.9257 0.8790 0.8839 0.8845 0.9253 1 Table 3a: Heavy Metal Concentration (mg/kg) in Soil Samples at Surface Depth 15-30cm Cu Mn Zn Fe Pb Cd Cr Ni As Hg A 5.32 9.61 11.84 14.25 13.09 3.09 3.06 4.42 2.23 1.82 B 4.96 9.84 11.98 15.26 12.23 4.08 4.48 3.89 2.2 2.26 C 4.84 8.92 10.82 12.63 11.92 3.67 3.76 4.52 2.26 1.88 D 4.84 8.45 12.38 14.33 11.58 3.73 3.35 4.28 1.97 1.97 E 2.68 3.42 4.72 6.64 4.81 1.87 1.07 2.05 1 1.07 F 1.84 3.64 3.38 6.86 4.57 1.76 1.08 2.02 1 1 Table 3b: Correlation of Heavy Metal Concentrations at Surface Depth 15 – 30cm Cu Mn Zn Fe Pb Cd Cr Ni Hg As Cu 1 Mn 0.9699 1 Zn 0.9836 0.9694 1 Fe 0.9558 0.9806 0.9835 1 Pb 0.9859 0.9930 0.9794 0.9732 1 Cd 0.9007 0.9315 0.9418 0.9446 0.9121 1 Cr 0.8995 0.9514 0.9232 0.9424 0.9213 0.9861 1 Ni 0.9632 0.9544 0.9580 0.9254 0.9772 0.8904 0.8805 1 Hg 0.9270 0.9596 0.9593 0.9755 0.9375 0.9868 0.9866 0.8875 1 As 0.9721 0.9900 0.9533 0.9482 0.9926 0.9027 0.9259 0.9739 0.9230 1 CONCLUSION The present study investigated the heavy metal contents of five different sites in soil contaminated with petroleum hydrocarbon in Ebudu community, River State, Nigeria. 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