The objectives of this study were to evaluate the health risk concern of some trace metals in selected borehole drinking water proximal to open dumpsites in Benin City. Borehole water samples were collected and analysed for trace metals using standard methods. Health risk and pollution indices were used to characterise the trace metals. The average daily dosage (ADD) results showed low concentrations of the trace metals in the various borehole sites. Oluku 1 had Mn (0.04), Zn (0.11) and Cu (0.01). Oluku 2 had Mn (0.43), Zn (0.18) and Cu (0.01) while Ikueniro 1 had Mn (0.05), Zn (0.17) and Cu (0.01) and Ikueniro 2 had Mn (0.04), Zn (0.15) and Cu (0.01). The hazard quotient (HQs) and hazard index (HI) values were < 1. The results of the Metal Pollution Index (MPI) revealed the values of Oluku 1 (4.6E-06), Oluku 2 (1.0E-04), Ikueniro 1 (1.4-05) and Ikueniro 2 (5.6E-06). The classification of the water were within class 0 and 1. The findings of this study have revealed that the trace metal contents found in the boreholes waters were within the safe limits as referenced. On this premise, the borehole waters were recommended safe for consumption without any health risk impact, consequent of no evidence of pollution.

ABSTRACT:The effect of toxic substances on aquatic lives from a wastewater indiscriminately discharged into the environment during oil and gas exploration activities in Nigeria is the focus of this study. A plant bioassay, the Allium cepa test, was used for the cytogenotoxicity screening of process water on root growth inhibition and chromosome abnormalities in the meristematic roots of the plant. Results of the physicochemical analysis of the wastewater collected from Nigerian Agip Oil Company (NAOC) facility at Ogboinbiri in Bayelsa State at the point of discharge into the environment showed that it had an unpleasant odour, was slightly alkaline (pH 7.72) and had high electrical conductivity (2793.33 µS/cm). Lead, manganese, iron, chromium and nickel were present at amounts (0.13, 0.33, 4.47, 0.17 and 0.10 mg/l respectively) above national (NESREA) and international (USEPA) limits for effluent discharge. Macroscopic evaluation of A. cepa cultivated in the wastewater resulted in significant (p<0.05) concentration-dependent root growth inhibition with an EC 50 value of 14.8 % at 96 h. Root tip cells of the onion bulbs processed for cytological studies by the aceto-orcein squash technique after exposure to the wastewater for 48 h at concentrations of 0.5, 1.0, 2. 5, 5.0, and 10% (v/v; wastewater/tap water) showed chromosomal aberrations at all concentrations. Statistical analysis of microscopic results show significant (p<0.05) concentration-dependent frequency of aberrant chromosomes and reduction of mitotic index. The findings in this study calls for proper treatment of process water before its discharge into water bodies to avoid cyto-genetic damages to aquatic lives.