Spatial and Seasonal Assessment of Heavy Metals in Surface Waters of the Middleton River in the Niger Delta, Nigeria

摘要

This study was aimed at assessing the bioavailability of heavy metals in the surface water of the Middleton river which is a tributary of the river Nun located in the Niger Delta area of Nigeria. Samples were collected at points within and around oil and gas installations in the area while control points were chosen farther from identified pollution point sources. Three replicate samples were collected for each sampling and control location on a biannual basis for two months (March and August 2017) to reflect the dry and wet seasons respectively. A total of forty-two surface water samples were analyzed for heavy metals using standard methods as given in APHA. Heavy metal variables which were examined indicated significant difference between the locations and the two seasons under study (p<0.05). Dry season heavy metals mean were: Fe (6.55 ± 2.36 mg/l and 7.39 ± 1.35 mg/l); Cr (0.43 ± 0.09 mg/l and 0.34 ± 0.02 mg/l); Mn (0.22 ± 0.31 mg/l and 0.02 ± <0.01 mg/l) and Zn (0.04 ± 0.03 mg/l and 0.01 ± <0.01 mg/l) representing five sampling and two control locations respectively. Wet season heavy metal mean levels were relatively lower when compared to the dry season and depicted values of Fe (4.91 ± 2.55 mg/l and 5.46 ± 2.09 mg/l); Cr (0.27 ± 0.05 mg/l and 0.23 ± 0.01 mg/l); Mn (0.13 ± 0.25 mg/l and <0.01 ± <0.01 mg/l) and Zn (0.01 ± 0.01 mg/l and <0.01 ± <0.01 mg/l) across five sampling and two control locations respectively. All other heavy metals analyzed such as Cd, Ni, Co, Pb, and Cu was found to be below the detection limit of the GBC Avanta PM A6600 - Flame Atomic Absorption Spectrophotometer. The iron and chromium levels found in the Middleton river exceeded permissible limits of DPR, FME, WHO and NESREA while chromium and zinc were within permissible limits of regulatory stipulations. Lower concentration of heavy metals in the wet season could be due to dilution effects while the absence of undetected heavy metals may depict that activities leaching out this heavy metals are not common in the study area.