Spatial and temporal variation of some heavy metals and total hydrocarbon content of soils from Okrika, Rivers State, Nigeria

Abstract

Spatial and temporal variations of some heavy metals and hydrocarbon content of soils from Okrika in Rivers State were carried out. Two crude oil-impacted communities in each of Okrika LGA (Alakiri and Abam) and Ogu/Bolo LGA (Bolo and Ogu) were selected for the study. One hundred and twenty soil samples were randomly collected from 4 locations, 30 samples each at depths of 0-5 cm, 6-10 cm and 11-15 cm .with the aid of a calibrated soil corer (50 mm in diameter) and covering both wet and dry seasons. Soil samples were taken to the laboratory for the determination of total hydrocarbon content (THC) and selected heavy metals. Total hydrocarbon content varied from 1343.2 – 85,565.11 mg/kg and that for heavy metals ranged from1.7-2.63mg/kg for cadmium 12.75– 30.48 mg/kg for lead, 1.98 -7.15mg/kg for copper and23.8 -47.0mg/kg for zinc. The study revealed that there were significant variations in the concentration of all the selected heavy metals across seasons but across study sites, differences were significant for copper and zinc only. Despite the obvious disparity in the magnitude of THC such differences were not statistically significant both across sites and seasons. Unlike copper and zinc, the concentration of lead and cadmium were above their stated limits thus suggesting a closer affinity to hydrocarbon. The observed concentration of THC which is far above the stated limit of 30mg/kg is indicative of severe hydrocarbon pollution in the study area and therefore the need for urgent remedial action.