EFFECTS OF SOLID WASTES ON HEAVY METAL CONCENTRATIONS IN SOILS AROUND OLD AND RECENT DUMPSITES IN PORT HARCOURT, NIGERIA.

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1 Continental J. Applied Sciences 3: , 28 Wilolud Online Journals, 28. EFFECTS OF SOLID WASTES ON HEAVY METAL CONCENTRATIONS IN SOILS AROUND OLD AND RECENT DUMPSITES IN PORT HARCOURT, NIGERIA. 1 Tubonimi J.K. Ideriah and 2 Victor O.T Omuaru 1 Institute of Pollution Studies, 2 Department of Chemistry, Rivers State University of Science and Technology, Port Harcourt. Nigeria. ABSTRACT Concentrations of As, Cd, Cu Cr, Ni and Pb in soils around two designated municipal solid waste dumpsites and a control site within Port Harcourt and its environs were examined. The results show that the relationship between the concentrations of metals with ages of waste dumps and depths of boreholes fitted log-log model. The models agree with statistical results and inferences. The results show no specific trend in the concentrations of metals with the ages of the waste dumps. The mean concentrations of Cd and Cu in the soils from the waste dumpsites exceeded tolerable limits. Chromium was the only metal that showed positively high correlation with depth. The concentrations of cadmium and copper, in soil exceed permissible limits of 3µg/g and 25µg/g respectively and are high enough to cause environmental pollution hazards while the other metals only contaminate the environment for now as their concentrations are below permissible limits. KEYWORDS: Solid waste, borehole, heavy metals, dumpsite, soil INTRODUCTION The need to asses the limitations of composts used on agricultural soils has created a demand for information on the availability of metals in municipal solid waste composts (MSWC). Land application is frequently recommended as a means to safely dispose or use municipal and agricultural wastes such as sewage sludges, sludge composts and animal manures (Walker, 1989). Julio (1994) reported that the metropolitan areas in the Third World generate almost 25 pounds (11.38kg) of wastes per person per day. Port Harcourt is highly industrialized and densely populated. Solid waste disposal practices in Port Harcourt and environs consist primarily of open dumping. Open dumps produce health and air pollution problems and are not acceptable methods of waste disposal (USEPA, 1991; Axel, 1994). Solid waste mismanagement problems have been identified in Nigeria. These problems range from soil system pollution and aquatic system pollution to air pollution, in addition to socio-economic decay (Okoko, 1998). Rain falling on land surfaces wets the soil and vegetation and either infiltrates the soil and percolates downwards towards the water table, or runs off the soil into streams and rivers. Lithologic logs of boreholes in Port Harcourt show that the first aquifer all through the area is unconfined and generally about 8 metres deep (Etu-Efeotor, 1981). A clay layer of variable thickness, depending on the location, confines the second aquifer. Most boreholes in Port Harcourt are drilled into the first aquifer as they rarely exceed 8 metres depth. The ground water level, measured from newly drilled borehole shows that water levels are close to the surface, commonly between metres. This study investigates the potential contamination of soils and ground water by heavy metals (As, Cd, Cr, Cu, Ni and Pb) in municipal waste dumps by assessing the effects of ages of dumpsites, seasons and depth of boreholes on the concentrations of the heavy metals. 114

2 MATERIALS AND METHODS BACKGROUND OF THE STUDY AREAS Two designated waste dumpsites and control and a control site were selected for this study which was conducted in 23 and 24 in Port Harcourt and its environs in Rivers State, Nigeria. These sites are situated along East West road measuring approximately 15m by 8m and lies between latitude N and longitude E; Eastern By-pass, measuring approximately 145m by 12m and lies between latitude and longitude 7 59 E. the University of Science and Technology, Port Harcourt which serves as control, lies between latitude N and longitude E. The map of the study areas is shown in Fig. 1. The dumping of wastes at the Eastern-West/Rumuigbo site lasted approximately 19 years, while dumping at the Eastern By-Pass lasted approximately 1 years. SAMPLE COLLECTION, PREPARATION AND ANALYSIS Samples were collected during the dry and wet seasons. The Dutch auger and trowel were used to collect topsoil samples (approximately -15cm) at each sampling site. In addition, two boreholes, 12 feet deep each, were dug by percussion drilling at East-West Road dumpsite. Soil samples were collected from the boreholes at five depths viz -1m, 1-2m, 2-3m, 3-4m and 4-5m. All the soil samples were transferred into appropriately labeled polyethylene bangs and taken to the laboratory for analysis. The soil samples were air-dried, ground, sieved to pass through a 1mm sieve (fine earth). Into a conical flask was put 1g of each of the sieved soil samples and digested with 1ml of 5% hydrochloric acid on a hot plate until 2-3ml of acid was left. The content was then filtered through Whatman No. 42 filter paper into a 5ml volumetric flask and made up to the mark with de-ionized water. 115

3 The concentrations of heavy metals were determined by a Buck Scientific Atomic Absorption/Emission Spectrophotometer 2A with a hollow cathode lamp. Table 1. Concentrations (µg/g) of heavy metals in soils at Easte-West Road/Rumuigbo waste dumpsite. (Dry and Wet Seasons) S/No Sample Code Heavy Metals (µg/g) As Cd Cr Cu Ni Pb Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet 1 EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS EWS RESULTS AND DISCUSSION The results, Tables 1-3, obtained generally showed variation in metal concentrations in soil in the two seasons. However no specific pattern was seen, as the dry season concentrations were higher in some cases while the wet season concentrations were higher in others. This observation is due to factors such as leaching, fresh dumps, plowing and scavenging. The relationship between the concentrations of metals in soil with ages of waste dumps and depths of boreholes are fitted to log-log models (Figs. 1-3). Log Y = b log X + c Where Y is the concentration of metals in soil at the waste dump, X is the independent variable (age or depth), b is the slope of the plot and c is a constant. The concentrations of metals are expressed as µg/g dry weight, ages as years and depths in metres. In this type of models, the thick line labeled ECL = 1 in the graph is the line of equal concentrations of metals with age or depth. This suggests an insignificant variation in these concentrations over several years or depths. This implies that the constituents of the refuse brought to the dumpsites are similar for the period under study. Points above this line indicate high or significant changes in concentrations of the metals. 116

4 The variations of metals concentrations with the ages of waste dumps are shown in Fig. 1. For all the metals, the model fit was significant at P<.1. The squared correlation coefficients for the models ranged from.5379 for chromium to.9937 for copper. As illustrated in Fig. 1 the regression equations for copper and lead are similar. The models show high concentrations of Cu, Pb and Cr in the wastes. The automobile parts and exhausts, spent batteries, electrical materials, etc in the wastes probably contributed to the high levels of these metals in the wastes dumps. The slopes of their regression equations are less than unity, indicating that their concentrations decrease with age. A similar trend was also apparent for As and Cd whose concentrations were low. Nickel, whose concentration variation was also low, was the only metal for which the slope of the regression equation was approximately unity, indicating constant or uniform changes in concentrations with the ages of the dumpsites. This suggests a similar rate of variation. These observations suggest that run off, topography, level of decomposition and scavenging as well as complexation influenced the availability of the metals. Thus metals whose concentrations were high were either high in the waste, complexed or minimally leached. However ANOVA showed no significant variation (F >.5) between ages and each metal concentration. Table 2. Concentrations (µg/g) of heavy metals in soils at Eastern By-pass dumpsites (Dry and Wet Seasons) No Sample Code Heavy Metals (µg/g) As Cd Cr Cu Ni Pb Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet 1 EBNS EBNS EBNS EBNS EBNS EBNS EBNS EBNS EBNS EBNS EBNS EBNS EBNS EBNS Table 3 and Fig.2 show the variations of metal concentrations in soil with depth at borehole 1. Except in the case of arsenic, the model fit was significant for all the metals at P<.1. The squared correlation coefficient of the models ranged from.3615 for cadmium to.841 for chromium. The concentration of chromium was significantly high and the slope of its regression equation was greater than unity, indicating that although its concentrations were high and increasing over the range of depths in this study, they decreased at greater depths. The concentrations of cadmium and arsenic were low. The concentrations of copper, nickel, and lead were high but the slopes of their regression equations are substantially less than unity. This indicates that their concentrations are highest at low depths. This is because the wastes do not penetrate to greater depths. These predictions are similar with the observations 117

5 from both t-tests and ANOVA, which showed significant variation (P <.5) between metal concentrations and depths. The variations of metal concentrations in soil with depth at borehole 2 are presented in Table 3 and Fig. 3. The models are statistically significant for all metals except As and Pb at P <.1. The squared correlation coefficients for the models ranged from.4859 for cadmium to.7723 for chromium. The slope of the regression equation for chromium is greater than unity, showing that its concentrations vary significantly with depth. The slopes of the regression equations for the other metals are relatively less than unity. This suggests that their concentrations are highest at low depths. These predictions are similar to the observations from both t-tests and ANOVA, which showed significant variation (P <.5) between metal concentrations and depths. Table 3.Concentrations (µg/g) of heavy metals in Borehole soils at East-West Road/ Rumuigbo waste dumpsite. S/No. Sample Code Heavy Metals (µg/g) As Cd Cr Cu Ni Pb 1 EWBH1 (-lm) (1-2m) (2-3m) (3-4m) (4-5m) EWBH 2 (-1m) (1-2m) (2-3m) (3-4m) (4-5m) The observations at the boreholes are similar and show that with the exception of chromium, the metals generally do not penetrate to high depths. The trend observed for chromium is in agreement with the results of ANOVA, which showed significant variation in metal concentrations with depths at boreholes -1 and -2 at P <.1. The case of chromium could be attributed to the geology of the study areas and probably inter horizon mixing. This is because the parent rock materials and wastes and other substances deposited on the surface of the soil mix and create a gradient of increasing metals concentrations. However, the gradual decrease in the squared correlation coefficients for each metal in soil at borehole -1 (main dump) to -2 (control) further indicates the influence of the waste dumps on the concentrations of the metals in the area. The concentration of As in the soils at the boreholes did not vary with depth. This observation agrees with the report that As is retained in -13m depth as a results of adsorption by oxides of Mn, Fe and Al (Tanji and Valoppi, 1989). The concentration of Cd in the soils at the boreholes increased steadily down to 3m depths and decreased down to 5m. This could be attributed to the texture of the soil, which affects its mobility. An analysis of variance (ANOVA) conducted on the variation of Cd with depth showed significant variation (F<.5) while there was no significant variation (F>.5) in the concentration of Cd with borehole location. The concentration of Cr in soil at borehole -1 was low at the top, it increased to 15.5µg/g and remained constant down to 4m and increased sharply at 5m depths. Similar trends (but with a drop at 4m) were observed in soil at borehole -2. The analysis of variance (ANOVA) conducted on the variation of Cr concentration with depth showed significant variation (F>.5) while the variation of Cr concentration with borehole location was not significant (F>.5). The observation here is contrary to the report that Cr does not penetrate below horizons rich in organic carbon at -6cm depth (Tanji and Valoppi, 1989). Large concentrations of As, Cu and Cr are reported by Lund and Fobian, 1991 to be retained in horizons with high contents of organic carbon. Also, neither Cr nor Cu is bound to a measurable 118

6 extent by cation exchange. The clay minerals play an indirect part in the retention of As, Cu and Cr (Lund and Fobian, 1991). The concentration of Cu in soils at all the boreholes decreased with depth. Cu is retained in soil at the - 13cm depths. Its retention in soils at the -6cm depths is associated with higher concentrations of oxides of Mn, Fe and Al (Tanji and Valoppi, 1989). The ANOVA showed no significant variation in the concentration of Cu with depths at F>.5. However, there was significant variation (F>.5) in the concentration of Cu in soil with borehole location. The concentration of Ni decreased steadily from the top to bottom in soil at borehole -1 while at borehole-2, the concentration was constant down to 3m and decrease down to 5m depths. The ANOVA showed no significant variation in the concentration of Ni in soil with depth at F>.5. However, there was significant difference (F>.5) in the variation of Ni with borehole location. The concentration of Pb in soil at borehole -1 decreased from the top with a sharp increase at 3m and decreased further at 5m depths. In soil at borehole -2, the concentration of Pb remained constant from the top to bottom. The ANOVA showed no significant variation in the concentration of Pb with depth at F>.5. However, there was significant variation (F>.5) in the concentration of Pb in soil with borehole location. The variation of metal concentrations in soil at the boreholes, in particular the higher concentrations of metals at some depths, are of environmental concern. For instance, the observation shows that metals like Cr have higher mobility than the other metals. However, the levels of metals in soil at the 5m depths indicate possible contamination of groundwater, which is of great concern, especially now that the dumpsites are being developed for public use. The degree of stabilization by organic matter determines the potential mobility of heavy metals (Leita and Nobili, 1991). The mobility of the metals also depends on the size distribution of the soluble metal species (Ayalon et al., 1991). The analysis of variance showed significant variation (F<.5) in metal concentrations between borehole -1 and borehole -2 with low positive correlation (r =.411). Only Cr showed high and positive correlation with depth in soil at the boreholes (r =.8938 in borehole -1 and.6111 in borehole -2). The correlations of the concentrations of other metals in soils with depth in boreholes were also high but negative. The binding of metals to humic substances seems to be an important factor that can potentially control their mobility in the soil. In general, the results tend not to agree with the report by Tanji and Valoppi, 1989 that heavy metal (Cd, Cr, Cu, Ni, Pb) accumulated on the surface 15cm soil owing to sorption by clays and hydrous oxides of Fe and Mn, complexation by soil organic matter and precipitation as inorganic minerals. The concentrations of cadmium and copper, in soil exceeded permissible limits of 3µg/g and 25µg/g respectively and are high enough to cause environmental pollution hazards while the other metals only contaminate the environment for now as their concentrations are below permissible limits. With reference to the ages of the dumpsites, this situation will persist for a long period and may increase with increased human (industrial, commercial and domestic) activities in the areas. CONCLUSION The findings of this study have shown that road traffic is not the major source of lead around the waste dumps. There were seasonal variations (although insignificant) in the concentrations of heavy metals. Most metals accumulated in the wet season owing to the dumping of fresh wastes and reduced scavengers during heavy rainfalls. The dumping of metallic substances and other wastes by scavengers, farmers, motorists and passersby contributed to the levels of metals in soils at distances from the waste dumps. In general, the levels of deposition, topography, run-off and scavenging influenced the concentrations of the heavy metals in soils at the waste dumpsites. The mixing of rock materials and the deposition of wastes and other materials on the surface of the soil suggest a concentration gradient for metals such as chromium through the borehole. Thus, heavy metals were found in the soils at the waste dumps, control and the boreholes. Once contaminated, the soils are liable to be polluted in the future since the metal concentrations decreased with age of waste dump. 119

7 The levels of metals obtained in the study may adversely influence human health since vegetables and crops locally grown on the waste dumps are continuously consumed. The levels of the metals could also pollute the waster supplied by streams, which are used for domestic purposes, recreation and inhabited by useful aquatic organisms. REFERENCES Axel, D. (1994): Gardening on garbage; opportunity or threat? ILEIA Newsletter, December 1994, Lausden, the Netherlands. pp Ayalon, O., Nishri, A. and Avnimelech Y. (1991): Distribution of soluble iron and zinc in leachates of municipal wastes. In Y. Chen and Y. Hader (Eds), Iron nutrition and interactions in plants 53-56, Kluwer Academic Publishers. The Netherlands. Etu- Efeotor, J.O. (1981): Preliminary hydrochemical investigations of subsurface wastes in parts of the Niger Delta, Nigeria. Jour. Min. Geol. 2 (1 & 2): Julio P. B. (1994): Working with waste in Latin America. ILEIA Newsletter, December Leusden, The Netherlands. Leita L. and Nobili, De. (1991): Water- soluble fractions of heavy metals during composting of municipal solid waste. Journal of Environmental Quality. 2 (1): Lund U. and Fobian A. (1991): Pollution of two soils by arsenic, chromium and copper. Denmark. Geoderma, 49; Okoko K.A.B. (1998): Organic waste as an agricultural resource. The Nigerian Journal of Oil and Polities (OPJON) vol 1 No. 2 Printed by Thompson (Nig.). Ltd., Victoria St. Port Harcourt. Tanji K. and Valoppi L. (1989): Groundwater contamination by trace elements. Agriculture, Ecosystems and Environment. 26:3-4, U.S.E.P.A. (1991): Environmental fact sheet. Yard waste composting EPA/53 SW Walker J.M. 1989: Assessment of sludge regulation assumptions: A framework for analysis. Biocycle. 3: Received for Publication: 8/1/28 Accepted for Publication: 27/11/28 Correspondence Author T.J.K Ideriah Institute of Pollution Studies Rivers State University of Science and Technology, Port Harcourt, Nigeria. Tujokid@yahoo.Com 12

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