DISTRIBUTION OF HEAVY METALS IN SOILS WITHIN THE VICINITY OF THE OYIGBO GAS FLARE SITE IN RIVER STATE, NIGERIA

Abstract

Six heavy metals were determined in soils to assess the impact gas flaring had on the micronutrient status of the soils. Soils were collected from the gas flaring site at Oyigbo in Rivers State Nigeria at 10m, 50m and 100m distance to the flare stack, from surface and subsurface depths. The soils were analysed for heavy metals using GBC-Avanta PM SN A6600 Atomic Absorption Spectrophotometer (AAS). Alterations in the micronutrient levels measured evidently point to the impact of the Oyigbo gas flare. However, concentrations of all the heavy metals were found to be within the target benchmark limits of Nigeria’s Department of Petroleum Resources (DPR) and the World Health Organization (WHO), except for Cd which recorded a concentration of 0.34  0.08 mg/kg at 0-10cm depth, 100m away from the flare and 1.18  mg/kg at 10-20cm depth, 10m away from the flare; these 10m results exceeded the 0.8mg/kg limit of DPR and WHO. One way analysis of variance (ANOVA) showed that the differences in the concentrations of the other metals (Fe, Pb, Zn, Cr and Ni) were statistically significant (P<0.05); this was validated by a complimentary post-hoc analysis using the Turkey’s Multiple Comparison Test. The trend in the concentrations was Cr > Ni > Fe > Pb > Zn > Cd. A geographically similar control soils collected from Choba, a community outside the vicinity of the gas flaring, had significantly lower concentrations of metals. Given the tendency of heavy metals to bio-accumulate and bio-magnify, it is recommended that periodic human health risk assessment be carried out in the study area to ascertain the toxic potency of these metals to the agricultural community.