Abstract
Heavy metals can be absorbed by plants resulting to contamination of other organisms in the food chain. This study was intended to determine heavy metals in soil, their mobility factor and impact on flora and fauna. To determine bioavailability of metal ions in soil chemical speciation and mobility factor indices were calculated. The level of Fe, Pb, Zn and Cd in readily available forms were assessed in dumpsite soils within mangrove forest in the Eagle Island and compared with control (i.e., relatively undisturbed soil). The aim of the study was to evaluate the impact and contribution of municipal waste discharge on alteration of soil quality and bioavailability of metals within the soil matrix. Samples of soil were collected in triplicate from five locations across the dump area while the control point was established at a less impacted area. Sampling was done in November 2018. Concentration of metal ion/species was analysed using GBC Avanta PM A6600 atomic absorption spectrophotometer. Soils of the sampling area were acidic with pH values ranging between 4.55 and 5.74. The most important heavy metal fractions in the dumpsite soils were; Fe (residual fraction, 53.75%), Pb (residual fraction, 42.58%), Zn (Fe-Mn oxide fraction, 46.85%) and Cd (carbonate bound fraction, 37.77%). However, the less impacted soil was predominantly affiliated to the residual fractions of Fe (68.75%), Pb (54.86%), Zn (37.45%) and Cd (51.51%). Heavy metal mobility factor indices reflected the order: (Cd>Pb>Zn>Fe) for soils of both the solid waste dumpsite and control areas. Despite the prevalence of heavy metals to the inert fractions, the significant affiliation of Cd to the readily mobile fractions of waste dump soils may suggest its release to have come from toxic constituents such as petroleum products that are associated with municipal wastes.
Highlights
The over-reliance of most communities on the open dump and landfill systems [1] as the primary practise for solid waste management is fast becoming an environmental problem
Soils of the mangrove forest in Eagle Island were acidic and this promotes the retention of heavy metal contaminants
Even though the most prevalent metal fractions within the soil system were the poorly mobile residual fractions, the significant associations of Cd to the carbonate bound fractions (37.77%) in soils of the waste dump remains a source of environmental health concern because of its potential to become bioavailable and transportable via the root system of mangrove trees that serve as spawning site for many organisms consumed by human
Summary
The over-reliance of most communities on the open dump and landfill systems [1] as the primary practise for solid waste management is fast becoming an environmental problem. The soil systems serve as sink for contaminants while heavy metals can persist in soil [2]. The presence of organic matter in soil emanating from municipal wastes can serve as metal chelators whereby they become non-bioavailable in the soil ecosystem. Waste in most areas can be liquid or solid. Liquid waste comes from industrial effluents discharged into the sea by petrochemical or manufacturing industries sited close to coastal areas. In the same vein solid waste are dumped on forest soil leading to contamination and pollution of the soil resulting in the formation of waste land
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