EVALUATON OF HEAVY METAL WATER QUALITY POLLUTION OF THE MIDDLE REACHES OF ORASHI RIVER, NIGER DELTA

Abstract

River water is an essential source of water for organisms in and around the river. The study was conducted to investigate river water quality pollution from ve stations between October 2017 and September 2019 with the aim of evaluating concentration of heavy metals in the aquatic ecosystem. Cd, Cr, Fe, Zn and Pb were selected. Heavy metals in water samples were determined using an Atomic Absorption Spectrophotometer. Concentration was < 0.001 mg L^-1 for Pb and Cd across all stations. Fe ranged from 1.54 – 4.97 mg L ^-1, Zn 0.01mg/l – 0.34 mg L^-1 . Cr was <0.001 in stations 1, 4 and 5, while stations 2 and 3 had their range and mean values to be 0.003 – 0.08 mgL^-1 . Results were compared with WHO permissible limits and NESREA standard. The concentration of Cd in all stations was less than WHO permissible limit of 0.05 mgL^-1 and NESREA standard of 0.01 mg L^-1 . NESREA standard indicates the study area is Cr while WHO indicates stations 2 and 3. All stations were Fe polluted when compared with both standards. Zn and Pb were below both standards indicating that the middle reaches of Orashi River are free of Zn and Pb. To determine the harmful effect of these metals in the study area two indices were selected. These are Contamination Factor (CF) and Pollution Load Index (PLI). The study site is in a low state of Cd and Pb pollution (1 ≤ CF). Fe was moderately polluted (1 ≤ CF < 3). Stations 1 and 4 was 1 ≤ CF suggesting low Cr pollution while Stations 2 and 3 experienced high level of Cr pollution (CF ≤ 6). Decreasing order of PLI was station 2 > station 3 > station 1 > station 4. It is therefore pertinent for the Ministry of Environment to monitor anthropogenic activities especially at Odiobor and Mbiama.