Abstract
Environmental and health risk posed by heavy metals from municipal landfill cannot be over emphasized. However, the toxicity and fate of metal in the soil is dependent on its chemical form and therefore quantification of the different forms of metal is more meaningful than the estimation of its total concentration. This study investigated the chemical form and potential hazards of heavy metal pollution at two municipal landfills in Sagamu, Ogun state, Nigeria. Soil samples were collected around the landfills and chemical form of Cu, Zn, Cd, Pb, and Fe were studied, using the Tessier Five-step sequential chemical extraction procedure. The results showed that Cu and Fe were speciated into residual fractions with averages of 23.9 and 31.3% respectively, while Cd and Zn were associated with Carbonate fractions with respective averages of 20.3 and 20.6%. The order of mobility and bioavailability of these metals are: Cd > Pb > Cu > Zn > Fe. A comparison of the result of total extractible metals with standard set by USEPA reveals that Cd and Cu level in the dumpsite soils are far above the critical permissible limit of 3.0 and 250 mg kg−1, respectively which potent a health risk. Assessment of soil pollution level using geoaccumulation index (Igeo) revealed that the landfill was extremely polluted by Cd (Igeo > 5). Pearson correlation and principal component analysis showed that there were no significant correlations (p < 0.05) among all the metals, suggesting that they are all from different anthropogenic sources. The cancer risk ranged from 1.36E−01 to 2.18E−04 and 5.82E−01 to 9.35E−04 for Children and Adult respectively. The level of cancer risk falls above the threshold values (10−4–10−6) which US Environmental Protection Agency considered as unacceptable risk. Based on the above findings, it was suggested that environmental management policy should be implemented to decrease the environmental risks.
Highlights
It is commonly accepted that soil contamination with heavy metals is potentially damaging to the ecosystem health.[1,2] Unlike organic pollutants, metals cannot be biodegradable and their residence time in the soil can be thousands of years
The total extractible Zinc contents in the dumpsite was higher than the control site but statistically insignificant (p < 0.05) and were within the permissible limits of 30–300 mg kg−1 for agricultural lands set by USEPA [54]
The results indicated that majority of Cu in the soil was associated with the residual fraction having an average of 23.9% which is similar to the reports of Iwegbue et al [56]
Summary
It is commonly accepted that soil contamination with heavy metals is potentially damaging to the ecosystem health.[1,2] Unlike organic pollutants, metals cannot be biodegradable and their residence time in the soil can be thousands of years. Solid waste management has become a serious environmental problem and a major growing concern for urban areas, especially in the developing parts of the world.[3] In most of the developing countries, it is commonplace to find huge waste dumps within residential and industrial areas and on shoulders of minor and major roads owing to inadequate regulatory framework and enforcement system This practice constitutes serious health and environmental concern due to the phytotoxicity effect of these metals to the plants and the animals feeding on such vegetables and plant based foodstuff.[4,5] waste deposited at open dumpsites and poor management of these sites could create a number of adverse environmental impacts including leachate, which could pollute underground soil bed.[6] Leachate from dumpsites are said to be of particular interest when it contains potentially toxic heavy metals.[7] These metals are known to bioaccumulate in soil and have long persistence time through interaction with soil components and enter into the food chain.[8]
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