Heavy metals were determined in topsoils around a major industrial estate co-located with a housing estate in the southwestern region of Nigerian. Samples were collected on three-monthly basis for 18 months, from the industrial waste dumpsites, industrial area, residential area, around an effluent channel, outskirts of the estate and control sites. Average levels of Cu (2850 ± 3340 mg/kg), Pb (768 ± 450 mg/kg) and Ni (105 ± 30 mg/kg) at the dumpsites were significantly higher than other locations. At the industrial area and effluent channels, Pb and Cr levels were slightly elevated compared with other metals. Metal levels at the residential area and outskirts of the estate were about the levels in the control. Generally, the degree of contamination within the vicinity of the estate was of the order Cu>Pb>Ni>Cd>Co>Cr. Average total bioavailable (non-residual) fraction of the metals consisted of 52.0% of the metal load, with this fraction for Cd and Pb being 73.9% and 60.7% respectively. Topsoils around the dumpsite were evidently polluted with high levels of copper and lead. Seepage of leachate from the dumpsite has the potential of contaminating ground water reserves. Improper disposal of industrial solid wastes appears to be the likely source of metal pollution in the industrial estate. Heavy metal pollution in the estate can therefore be significantly reduced by prompt and proper disposal of generated solid wastes, and the application of particulate scrubbers in the industries.
The mobilization of heavy metals into the biosphere through industrial activities is an important process in the geochemical cycling of metals. This is very evident in urban areas where various industrial sources release large quantities of heavy metals into the atmosphere and soil [1-5]. Some of the pathways of these metals into the soil are via dustfall [6-9], fly ash [
Despite growing rates of industrialization, many developing third world countries pay too little attention to environmental issues. This is evident in the location of many industrial facilities near residential areas and the non-availability of adequate regulatory and enforcement measures to guard against pollution. One of such industrial facilities co-located with residential areas is the Ota Industrial/Housing Estate in the southwestern region of Nigeria (
pollution, using the accumulation factor (AF) values.
The Ota industrial/housing estate, located on latitude 6˚32'N and longitude 2˚57'E, is sited on a 22.8 km2 expanse of land in tropical southwestern region of Nigeria (
Topsoils were sampled from three core industrial areas (SL-IND), three residential areas (SL-RSD), beside two liquid effluent channels (SL-EFL) and two refuse dumpsites (SL-REF). Two other locations were on the outskirt of the estate (SL-OST) where there were no waste dumps. Control samples were obtained from other residential areas located about 1 km from the industrial estate and not affected by industrial activities. Field sampling and analysis were conducted on a quarterly basis for a period of 18 months. Each sample was obtained by compositing surrounding topsoil into a polythene bag with the aid of a plastic scooping trowel.
The soils were air-dried in a clean room in the laboratory and then passed through a 2 mm mesh sieve. Soil pH was determined by the electrometric method using a 1:1 soilwater mixture [
Accumulation factor (AF) for each metal at each location was calculated to determine the degree of contamination at the sampling locations. This is the ratio of average metal concentration at any one sampling location to the concentration at the control point. The AF is a good index for assessing soil environmental quality [27-31]. In addition, analysis of variance (p = 0.05) was conducted to establish statistical relationships among metal concentrations at different sampling locations.
Metal concentrations in topsoil of the industrial estate are shown in
*SL-IND—industrial area, SL-RSD—residential area, SL-OST—outskirt of the estate, SL-EFL—beside effluent channels, SL-REF—dumpsite, SL-CTR— control. See
*SL-IND—industrial area, SL-RSD—residential area, SL-OST—outskirt of the estate, SL-EFL—beside effluent channels, SL-REF—dumpsite, SL-CTR— control. **Mean ± Standard Deviation (Range).
*SL-IND—industrial area, SL-RSD—residential area, SL-OST—outskirt of the estate, SL-EFL—beside effluent channels, SL-REF—dumpsite, SL-CTR— control.
corded here are much higher than previously observed at another industrial estate in the nearby city of Lagos where the corresponding AF values were 15.0, 28.1 and 13.1 [
mg/kg) and Cu (589 mg/kg) levels in this study exceed the Norwegian and Swiss guide values. Average Pb, Cu, Cd, Cr and Ni in the residential and industrial areas of the study area in
Average metal levels in this study were compared to those obtained in other areas with similar industrial activities. Average Pb level (199 mg/kg) in this study is higher than the 102 mg/kg reported for soils of the Upper Silesia industrial environment in South Poland [
The study reveals that heavy metal pollution of topsoil is significant in the industrial estate. It also points to wastedumping as the most important source of the contamination. The soil characteristics may enhance migration of the metal contaminants into ground water, although the exchangeable fraction is limited. Preventive and remediation actions may be required to reduce present levels of contamination to within safe limits. Such actions must focus on the identified dumpsite point sources, in addition to other measures. This may be managed by prompt and proper disposal of solid wastes, installation of particulate scrubbers, and regular monitoring of soil quality to comply with regulatory standards.