TRACE METALS IN SELECTED FOOD CROPS IN SMALL-SCALE OIL-REFINING AREAS OF IKOT-ABASI, AKWA IBOM STATE, NIGERIA

This study aimed to determine the effects of illegal crude oil refining on soils and cultivated root crops at Ikot Abasi, Nigeria. Tuber crops with their leaves and stems as well as soils from affected areas were sampled and analysed for trace metals (Pb, Zn, Cu, Cd and As) using Atomic Absorption Spectroscopy (AAS). Transfer factors (TF) for the metals between the soils and various plant parts were estimated and pollution load indices (PLI) of the metals in soils were calculated. Analysis of results showed that the levels of Pb, Zn, Cu, and As in plant parts were below permissible limits while Cd from the plants parts were above standard regulatory limit with values between 11.24 µg/g and14.82 µg/g. In all cases the level of heavy metals in the parts of the food crops followed the order: leaves>stem>tubers. The order of metal concentration in soils was Zn ˃ Pb ˃ Cd ˃ Cu ˃ As. The concentrations of the heavy metals in the soils were higher (P<0.05) in the oil refining (test) soils compared to the controls. Conversely, the levels of metals in plant parts were higher in the controls than in the study area. This revealed that crude oil inhibited uptake of trace metals by the plants. Although trace metal levels in the soils were generally lower than the standard regulatory limit there was heavy metal contamination as observed from the estimated PLIs. Analysis of metal transfers had shown that there had been high accumulation of Cu in the selected food crops, to levels which far exceeded the recommended tolerable levels proposed by FAO/WHO. It is recommended that trace metals in food crops cultivated in oil refining communities should be continuously monitored to prevent their excessive build-up in the food chain. Remediation treatment on farmlands as well as overall education of the host communities on the possible health impacts of illegal crude mining is recommended.