Analysis of Heavy Metals in Some Food Crops and Soils Impacted with Crude Oil in Southern Nigeria

Abstract

Mercy Uwem Useh* and Eno Linus

The contamination of food crops grown in crude oil-impacted soils by heavy metals is becoming alarming due to incessant
oil spills. Some physicochemical and heavy metals (Fe, Ni, Cr, Pb, Cd, Zn, and Cu) analyses of crude oil-impacted soils from
southern Nigeria and some food crops are grown on them were carried out using standard analytical procedures. The soil samples were collected from different communities (Atia, Ntafre, Ntak Ifaha, Esitikeme, Awah) and a control sample was also collected from a nearby non-oil impacted farmland in Mkpanak community, all in Ibeno Local Government Area of Akwa
Ibom State, Nigeria. Some food crop samples (Manihot esculenta Crantz, Dioscorea alata, Zea mays L., Musa paradisiaca and
Colocasia esculenta) were randomly collected simultaneously along with the soil samples from all sites. The results revealed
that the soils’ pH varied from 5.35±2.10 to 6.18±0.00 which indicated that the soils under study were acidic while that of the
control was 7.94±1.52. The organic matter (OM) content in all the impacted soil samples was higher (12.95±0.35 % to 17.05±4.28 %) compared to the control soil (6.74±1.30 %) sample. The concentrations of the heavy metalsin the soils in terms of abundance were in the order: Fe > Zn > Ni > Cu > Cr > Pb > Cd which showed that Fe is the most sufficient. It was observed that most of the studied crops especially Manihot esculenta C. had values of heavy metals higher than the values recorded for their respective soil
samples. Also, the levels of all the studied metals exceeded the permissible limits set by WHO/FAO except for Zn and Cu. However,
the soil-to-plant transfer factor (TF) showed that the highest TF recorded was in Zn, with most values above 1 followed by Cr and Cd. This is an indication that Zn, Cr and Cd were the most bio-available metals. This signified that residents could be exposed to substantial health risks associated with heavy metals via the consumption of these food crops.