Bioaccumulation of heavy metals by Vigna unguiculata (cowpea) grown on Olusosun Dump Site soil, Lagos, Nigeria

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  • July 4, 2019
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As a result of African beliefs that dumpsite soils improve plant growth, many local farmers have relied on growing crops on dumpsite soils. For this purpose, this study investigated the presence and level of heavy metals (HM) in Olusosun dumpsite soil and Vigna unguiculata grown on the dumpsite, with a particular reference to the relationship between the dumpsite soil HM content and the rate of bioaccumulation by plants and also, a comparison of the HM levels in the test plant with WHO and NAFDAC standard for HM in food and vegetable products. HM concentration was determined through Atomic Absorption Spectrophotometer (AA 6800, Shimadzu) and the seeds of V. unguiculata were obtained from Borno State Agricultural Development Program (BOSADP). The result obtained showed the presence of Zinc (Zn), Lead (Pb), Chromium (Cr) and Nickel (Ni) in the dumpsite soil and also in the test plant. Zn was detected to have the highest concentration (12.25 Mg/Kg) while Ni was the lowest (6.1 Mg/Kg). A comparison between the level of HM obtained and the WHO/NAFDAC standard for HM in food and vegetables revealed Zn level in the test plant was within the standard (50-60 Mg/Kg). However, Pb, Cr and Ni were detected to be above the standard (2.0 Mg/Kg) and therefore may pose serious health risk if consumed. The transfer factor (Tf) revealed that plants grown on Olusosun dumpsite soils accumulated higher HM (1.30-9.20). Generally, the result shows that there was an increase in the level of HM in all the sample sites and test plants than the control. This research clearly indicated those consuming V. unguiculata grown on Olusosun dumpsite soil are at risk of Pb, Cr and Ni poisoning.

Keywords: Heavy metal, Vigna unguiculata, Bioaccumulation and Health risk