Atmospheric Deposition of Soot and Heavy Metals from Gas Flaring into Surface Waters of Ebocha, Rivers State, Nigeria

Abstract

The continuous combustion of associated gas during crude oil production emits vast quantities of soot, greenhouse gases, and trace metals into the atmosphere. These emissions contribute to air quality degradation, acid rain formation, and the contamination of terrestrial and aquatic ecosystems through dry and wet deposition processes. This study investigates the atmospheric deposition of soot and heavy metals originating from gas flaring into surface waters of Ebocha, Rivers State, Nigeria. Twelve surface water samples were collected from four stations located 0.5, 1.0, 2.0, and 5.0 km from the flare site to assess spatial variations in pollution levels. Physicochemical parameters such as pH, temperature, electrical conductivity (EC), and total dissolved solids (TDS) were measured in situ, while concentrations of Pb, Cd, Ni, Cr, and Zn were determined using Atomic Absorption Spectrophotometry (AAS) after acid digestion in accordance with APHA (2017) standards. Results showed that pH values ranged between 5.62 and 6.74, indicating slightly acidic conditions, while EC and TDS ranged from 224.5 to 483.7 µS/cm and 105.3 to 243.6 mg/L, respectively. Heavy metal concentrations decreased with increasing distance from the flare site and followed the order Zn > Ni > Pb > Cr > Cd, with mean values of 0.628, 0.097, 0.118, 0.066, and 0.032 mg/L, all exceeding WHO (2017) and FAO/WHO (2001) guideline limits for potable water. Strong positive correlations (r = 0.82–0.94) between EC and metal concentrations, and inverse correlations with pH (r = –0.69 to –0.74), confirmed the influence of acidic atmospheric fallout from flaring emissions. These findings demonstrate that continuous gas flaring substantially enriches surface waters with toxic metals and soot, posing ecological and public health risks due to bioaccumulation and persistence. The study recommends continuous monitoring, strict enforcement of emission controls, and adoption of gas re-injection technologies to mitigate ongoing environmental degradation in the Niger Delta.