Concentrations of heavy metals in untreated produced water from a crude oil production platform in Niger-delta, Nigeria

Abstract

The various stages of petroleum industrial activities are linked with at least a by-product, residue or waste. One of such is an effluent from the mining of crude oil and gas, known as produced water, which contains varying quantities of hydrocarbons and heavy metals, thereby making it to require proper treatment in order to reduce the contaminants load to acceptable levels before being discharged into the environment. However, there are reports that this by-product is sometimes discharged untreated into Nigeria’s coastal waters. This study was therefore carried out in order to contribute to efforts at sensitising the various stakeholders concerning this challenge. In carrying out this study, samples of untreated produced water were obtained from a crude oil production platform in Rivers State, Nigeria, using chemically clean amber glass bottles, properly covered with Teflon-lined lids to prevent contamination, transferred to the laboratory in ice boxes, and subjected to atomic absorption spectroscopy for heavy metals detection and quantification in line with standard laboratory procedures. Results showed that the following detected heavy metal ions i.e., Iron, Copper, Manganese, Cadmium, Lead, Nickel and Chromium had mean concentrations, in mglitre^-1, of 3.9, 2.5, 2.4, 2.7, 1.4, 2.6 and 1.2 respectively. These values were comparatively higher than the documented required limit for these metals in drinking water and effluent to be discharged into inland water. The prescribed limits for drinking water by World Health Organization (mglitre^-1) are as follows: Fe (2.0), Cu (2.0), Mn (0.4), Cd (0.003), Pb (0.01), Ni (0.07) and Cr (0.05).

Key words: Coastal pollution, Produced water, Toxic metals, Crude oil, Petroleum gas