Heavy Metal Concentr...

Illegal crude oil refining, theft, and sabotage, amongst others, have assumed an advanced stage within the Niger Delta region, culminating in degradation of major biophysical environmental matrices such as soil and vegetation. Farmlands in Elele-Alimini and Ibaa in Emohua Area, Ogbodo in Ikwerre Area and Umuanyagu (control) in Etche Area of Rivers State, Nigeria, were sampled in this study. A total of fifty (50) sampling points in both test and control locations were randomly selected using a standard spatial (grid-based) sampling technique. Soil and plant samples within the farmlands were collected and analysed in the laboratory for heavy metals using an atomic absorption spectrophotometer (AAS). Mean values of Zn, Pb, Cd, Ni, Mn and Cu in test soil during the dry and wet seasons were in the ranges 7.34-13.37 mg/kg and 6.06-11.39 mg/kg; 4.53-5.87 mg/kg and 3.68-5.39 mg/kg; 1.78-2.85 mg/kg and 1.68-3.11 mg/kg; 5.09-6.02 mg/kg and 4.29-5.62 mg/kg; 103.60-149.1 mg/kg and 101.05-156.51 mg/kg, and 3.51-6.96 mg/kg and 2.77-3.70 mg/kg respectively. Mean values of Zn, Pb, Cd, Ni, Mn and Cu in test plants during the dry and wet seasons were in the ranges 13.26-69.30 mg/kg and 8.40-42.65 mg/kg, <0.001-6.61 mg/kg and <0.001-5.19 mg/kg; <0.001-0.51 mg/kg and 0.13-0.49 mg/kg; 0.36-1.99 mg/kg and <0.001-1.15 mg/kg; <0.001 mg/kg and <0.001; 13.14-139.74 mg/kg and 14.53-67.56 mg/kg, and 1.94-6.59 mg/kg and 1.28-5.48 mg/kg respectively. Levels of heavy metals generally were: Mn > Zn > Ni > Pb > Cu > Cd. Human health risk assessment, EDI values for all metals during dry and wet seasons fell within the recommended reference oral dose, except for Pb and Cd in adults and children at some study locations. To avoid future contamination, it is advised that artisanal refining activities in the area be avoided.