Evaluation of the extent of pollution of discharged oil field brine in the Bonny estuary, Niger Delta, Nigeria

Abstract

This is an assessment of the degree of effects of discharged produced water in river and sediments of the Bonny estuary, Niger Delta. It involved seasonal analyses of twenty-two (22) water and thirty-four (34) sediment samples from the Bonny River. The physicochemical properties (i.e., hydrocarbon content, heavy metals, and other inorganic constituents) of the water samples were examined, while the sediments were inspected for heavy metals and organic hydrocarbon constituents that may have been sourced from the discharged produced water. In addition, the principal component and cluster analyses, index of geoaccumulation, and pollution load index plots were utilized to deduce the degree of pollution, source, and distribution of these contaminants. From the results of the analyses, the Bonny seawater is contaminated with nitrate, phosphates, nickel, ammonia, and phenols in dry season, whereas nitrate, sulfate, phosphate, total nitrogen, total petroleum hydrocarbon (TPH), and heavy metals—zinc and lead—are observed in the rainy (wet) season. Similarly, the sediments are contaminated with benzene, toluene, ethyl benzene, xylene, polycyclic aromatic hydrocarbon, TPH, phenols, and heavy metals in both seasons. Considering the outcomes of these analyses, it is evident that the composition and quality of seawater and sediments of the Bonny estuary have been strongly influenced by produced water discharges in the area.