Assessment of Dumpsite Soils in Mangrove Forest at Eagle Island, Nigeria: It’s Effect on Potential Bioavailability of Heavy Metals in the Environment

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.