Abstract
Agricultural produce resulting from the cultivation of polluted soil can result in undue exposure and health hazards for its consumers at different level along the food chain. Available literature has shown that maize absorbs and accumulates toxic heavy metals from polluted soils. This study was designed to determine the concentration of lead (Pb), cadmium (Cd) and iron (Fe) within the leaf, stem, grains and root of maize grown on Ori-Ile battery waste dumpsite, Olodo, Ibadan Nigeria. Soil samples were collected every two months (March 2008 to July 2009) from the waste dumpsite and along the direction of the garden at 5m interval from the edge of the waste dump site. To determine the levels of uptake and accumulation of Pb, Cd, and Fe, maize was planted in a nearby house garden, situated within 25m distance away from the waste dumpsite and the root, stem, leaf and grains were harvested at maturity. All soil samples collected and the harvested maize parts were analysed for Pb, Cd, and Fe. Concentrations of Pb, Cd and Fe in soil were found to range from 3265.8±517.8 to 4351.3±1068.2; 163.96±23.2 to 258.38±123.1; 7712.90±473.8 to 8130.00±808.4 mg/kg respectively. These were significantly higher than values obtained from the reference soil (157.0±39.8, 2.2±1.2, 976.3±353.9 mg/kg respectively) and National Environmental Standard Regulation Agency (NESREA) limits (164mgPb/kg and 50mgCd/kg). Also, soil contamination factor values obtained were greater than 6 and this indicated severe contamination. Concentrations of Pb, Cd and Fe in maize-parts were significantly higher (P ≤ 0.05) than those cultivated on the reference site soil. Roots had the highest concentration of Pb (40.95±1.98 mg/L) and Cd (2.84±0.19 mg/L). In all maize-parts, bio-accumulation factor of the heavy metals was less than 1. Overall, these results have shown that the levels of metals in soil were several folds above the limits set by NESREA. Also, the range within the analysed plant parts was above the normal limit recommended for plants. High accumulation of heavy metals found in the soils of Ori-Ile battery waste dumpsite, Olodo, Ibadan bio-accumulated in maize-roots. Therefore, maize root is actively involved in phyto extraction of heavy metals from contaminated soils.
Highlights
Land contamination and degradation is a threat to sustainable agricultural development and food security in developing countries [1]
The results indicated that Pb and Cd concentrations exceeded the Environmental Quality Standards set by National Environmental Standard Regulation Agency (NESREA) for soils in Nigeria (Table 2)
Heavy metal accumulation in soils and plants is of increasing concern due to the potential human health risks [28, 60]
Summary
Land contamination and degradation is a threat to sustainable agricultural development and food security in developing countries [1]. Heavy metals tend to persist in the environment indefinitely [9] and get accumulated over time in soils and plants. They could have a negative influence on physiological activities of plants, determining the reductions in plant growth, dry matter accumulation and yield [10]. Excessive accumulation of heavy metals in agricultural soils often lead to elevated heavy metal uptake by crops, and affect food quality and safety [11]. Some of the heavy metals such as Pb and Cd are toxic to plants and animals, even in trace concentrations [16]; and exposure to some of them is normally chronic due to food chain transfer [17]. Excess Fe can result in dark green foliage, stunted growth of tops and roots, dark brown to purple leaves on some plants [20]
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