Solid waste trash in urban environments is the nature-derived products of man’s daily undertakings, especially in populated, bustling cities of developing nations. Whilst urbanization leads to a rapid rise in human population growth, it equally mounts pressure on production to meet demands. Consequently, the increasing multiplication of wastes, coupled with inappropriate waste discharge options continues to pose a major health challenge for the government and people to tackle 1. Waste dumping, though a popular waste management practice, is among the less effective and desired options of managing trash. In spite of this, vast tonnes of waste are still being junked in open-air solid waste dumpsites globally 12. The limited capacity to reprocess wastes, especially in economically developing nations is reason for having a higher fraction of municipal debris going to open waste dumps 3. Often times, these wastes are not segregated into their decomposable and non-decomposable fractions 4. In fact, tendencies are that numerous metropolitan cities of emergent countries will continue to be hounded with the varying adverse ecological changes posed by this waste management practice 5. Quite frankly, the Nigerian perspective for dealing with wastes does not reflect any positive deviation from this trend as six of the largest dumpsites in Africa are situated in the metropolitan cities of Lagos (Oluosun, Solous 2 and Epe), Ibadan (Awotan-Apete and Lapite) and Port Harcourt (Eneka) open dumpsites 16.

Municipal waste dumping has become an urban menace due to limited infrastructure to cater for the rapid development of sprawling towns and cities. Many cities are unable to provide basic social utilities spanning from housing, portable underground water and effective handling of solid squanders, thereby resulting to the mounting heaps of trash in sanitary landfills and open-air dumps, serving as hotbed for disease-carrying rodents and insects. Garbage dumping grounds are dotted within, and at outlying areas of Nigerian towns, which as a result of poor waste handling methods have continued to compromise the health conditions of those residing within close proximity of scrap sites. A decimation of self-reported illnesses has been reported with extended distances of human residence from dump grounds 7, while land-fills in the vicinity of riverine communities may often result in overwhelming eutrophication processes 8.

Every day, several million tons of municipal scrap wastes are been disposed worldwide, with methane (a greenhouse gas (GHG)) making up about half the fractional constituent of land-fill gas (LFG) and responsible for over 10% global emissions of methane. The rising levels of atmospheric methane, one of the GHGs responsible for global warming is sufficient reason for governments, especially of third-world countries, to enlighten and initiate modern waste reprocessing operations, reduce GHGs and similar atmospheric emissions by trapping as land-fill gas energy, one that will not only serve as an ameliorative policy to reduce the impact of ozone depletion but also aid in restoring the environment and decimating associated public health hazards, alongside improving energy independence and exploiting other socio-economic benefits 1910.

The high mobility and bioavailability of contaminant heavy metals in dump yards increases their risk of infiltrating surrounding ground water systems and stretches their toxic impact through the food chain. Most especially, lead and cadmium are among the metals on “red alert” based on their environmental unfriendliness, bio-accumulation tendencies and cumulative toxicant effects to body tissues and organs. Even trace contamination of soil by heavy metals can have far-reaching effects on the health of man and his environment, whilst constituting prolonged menace to water and ecosystems, or absorbing through plant roots and other biodiversity growing in abandoned waste dumpsites 4111213141516. The menace from leaching municipal waste dumps is proliferated depending on the waste content, bulk volume of trash, lifetime of waste dung, prevailing thermal conditions, water content, oxygenation levels, soil formation type and comparative separation from human and aquatic habitation 131718.

The key operational shortfalls that were observed at dumpsites in the Niger Delta were poor sanitary practices, poor manning and monitoring of daily activities, an evident lack of tools and equipment required for executing routine cleaning operations, the absence of anti-contamination apparatus for detoxifying leached dump effluents, unavailability of gas recollection systems, non-existent fire-fighting instrument, dearth of environmental buffer areas and the absence of barricades around waste dump yards, followed by the lack of safety training for waste handlers and the likelihood of their exposure to disease conditions 19. About 2.1% of responses from some interviewed Yenagoa residents revealed good recognition of waste handling procedures (95.4%), utilization of waste receptacles (86.7%), relatively effective waste collection by environmental sanitation authorities (70.4%), practice of open-air incineration (6.3%), dumping into rivers and storm water drains, or by roadsides (5.0%), stacking at backyards (2.1%) 20.

Apart from the atmospheric concomitants that are released from open dumpsites, the surrounding soils and leachate from trash dumpsites pose potential pollution problems by way of reducing soil fertility and compromising surface and underground water quality as a result of the vertical delineation of micro-pollutants such as trace/heavy metals, persistent organic pollutants and anions through the soil strata. From the foregoing, this study aims to assess the extent of environmental risks posed by some soil available trace metals within vicinity of the Tombia/Amassoma dumpsite by applying some heavy metal pollution indices.

Table 3 presents the heavy metals in soils around the dumpsite along Tombia-Amassoma road in Yenagoa metropolis, while the Spearman’s rho correlation matrix of heavy metals in dumpsite soil is highlighted in Table 4. Lead concentrations ranged from 5.597 to 109.460 mg/kg, 1.763 to 75.427 mg/kg and 1.493 to 67.470 mg/kg for top soils (0.3 m), mid-depth soils (0.5 m) and bottom soils (1.0 m) of dumpsite contaminated soils respectively. Cadmium levels reportedly between 0.550 and 3.143 mg/kg, 0.247 and 4.237 mg/kg and 0.133 and 2.807 mg/kg for top soils (0.3 m), mid-depth soils (0.5 m) and bottom soils (1.0m) of the dumpsite contaminated soils respectively. Finally, chromium concentrations ranged from 8.377 to 22.183 mg/kg, 6.443 to 25.367 mg/kg and 5.200 to 14.877 mg/kg for top soils (0.3 m), mid-depth soils (0.5 m) and bottom soils (1.0m) of the dumpsite contaminated soils respectively (Table 3).

On the other hand, only top soils (0.3 m) were collected for the control locations with values ranging from lead (1.660 to 2.957 mg/kg), cadmium (0.210 to 0.223 mg/kg) and chromium (9.453 to 10.107 mg/kg) respectively. Apart from the top soil of dumpsite location 1 (0.3 m), lead in soil was predominantly within the Department of Petroleum Resources (DPR) target value of 85 mg/kg. Also, soil chromium was within DPR target value of 100 mg/kg for all dumpsite-contaminated locations. However, all three (3) soil depths of sample location 1 and top soil (0.3 m) of location 2 showed cadmium values exceeding the DPR target concentration. In spite of the conformance of metal concentrations recorded in the dumpsite to DPR intervention levels, it is pertinent to identify concentrations exceeding target values as being environmentally significant and possessing hazardous potential. On the other hand, soils of both control locations revealed relatively lower heavy metal concentrations, with all values being within stipulated DPR target and intervention levels. All other sampling locations and depths were within the specified regulatory target and intervention levels of 0.8 and 12 mg/kg for cadmium in soil (Table 3) 31.

Most notably is the fact that all sampled depths of location 1 and the top soil of location 2 consistently showed significant difference (p < 0.05) for all the metals been analyzed. The locations with no significant difference (p > 0.05) includes: midpoint (0.5 m) and bottom soils (1.0 m) of locations 2 and 3 for lead and cadmium, and bottom soils (1.0 m) of locations 2 and 3 for chromium (Table 3). In addition, the strongest and weakest positive correlations were between lead and cadmium (r = 0.855, p < 0.01), and lead and chromium (r = 0.787, p < 0.01) respectively, with cadmium also showing positive correlation with chromium (r = 0.829, p < 0.01) (Table 4).

Heavy metal levels in the study area is higher than values previously reported in soils around the embankment of effluent wastewater retention pits in the Niger Delta 32, the oil flow station at Imiringi community in Bayelsa State 21, Rumuolukwu community oil spill site 22, residual fractions of dumpsite soils in a mangrove forest at Eagle Island 33, crude oil contaminated soils of Bdere community in Ogoni land 3435. However, chromium values in this study was lower than earlier reported by 36 for soils from an abattoir dumping site. Statistically, the soil metals showed positive correlation with each other, suggesting that they may be from similar source 213738. The correlation trend of heavy metals in sediment, as reported in this study, corroborates the report of 21 where lead, nickel and iron depicted positive correlations. Similar to the findings of 39 where statistical analysis revealed statistical variations in metal levels of dumpsite soils, this study revealed similar trend among metal concentrations and locations.

Obviously, there is a connection between soil quality and heavy metal levels 3940414243. Most metal contaminants often depict elevated levels of distribution spread during the dry season 142236. Hence, the concentration of heavy metals in soils within vicinity of open-air dumpsite is observed to be higher than those collected from natural uncontaminated environments 1433. Furthermore, studies have shown that the levels of these contaminant metals in soils around municipal waste dumpsites are not dependent on the life time of the dump area but on the origin/cause, make up and terrain of the waste dump 44.

The soil quality status of the Tombia-Amassoma waste dumpsite is observed to be severely impacted by the leached waste run-offs resulting in reasonable vertical seepage of heavy metal micro-pollutants within the soil profile, even up to the depth of 1 m. Compared to the non-impacted control locations, the waste dump site showed relatively higher distribution of test metals, especially at location 1, where two non-essential metals (lead and cadmium) recorded toxic concentrations exceeding stipulated regulatory limits. There was statistical significance across the varying sample locations which depicted varying contamination point sources. This may have emanated from the divergent origins of dumped waste. Lead and cadmium were strongly associated contaminants, both reflecting elevated environmental metal loading, potential ecological risk and significant contamination levels. In view of the prevailing metal contamination within the impacted soil environment, it is pertinent that proactive steps are taken by relevant local environmental authorities and stakeholders to ensure that proper sanitary conditions are kept, an environmental remediation plan is instituted and more effective waste management options are adopted in order to cope with emerging waste generation challenges which will likely persist as a result of increasing urbanization and industrialization of Yenagoa metropolis.