Low-molecular-weight Polycyclic Aromatic Hydrocarbons as Indicators of Petroleum Contamination and Ecological Risk in Ataba–bodo Estuary Sediments, Niger Delta

Abstract

Background: Polycyclic aromatic hydrocarbons (PAHs) are persistent organic contaminants capable of accumulating in aquatic sediments and posing ecological concerns in estuarine environments exposed to petroleum-related and other anthropogenic activities. The Ataba–Bodo estuarine environment occurs within the Niger Delta, where intensive human activities may influence sediment quality. Aim: This study assessed the occurrence, spatial distribution, compositional characteristics and ecological risk associated with five low-molecular-weight PAHs in sediments of the Ataba–Bodo estuary, southern Nigeria. Materials and methods: Surface sediment samples were collected from eight stations comprising four stations at Ataba and four at Bodo. Three replicate samples were collected per station. Samples were prepared and extracted for chromatographic determination of naphthalene, acenaphthylene, acenaphthene, fluorene and phenanthrene. Concentrations were expressed as µg/kg dry sediment. The total concentration of the five target compounds (Σ5LMW-PAHs), the relative contributions of individual compounds and spatial distribution were determined. Ecological risk was evaluated using the risk quotient approach. Results: All five target LMW-PAHs were detected across the sampling stations. Naphthalene was the dominant compound, with concentrations ranging from 31.45 ± 0.63 to 89.62 ± 1.78 µg/kg, followed by phenanthrene, which ranged from 29.64 ± 0.61 to 71.46 ± 1.39 µg/kg. The Σ5LMW-PAH concentration ranged from 81.27 ± 0.93 µg/kg at ATB-3 to 221.07 ± 2.42 µg/kg at BOD-2. The mean Σ5LMW-PAH concentration was higher at Bodo (171.97 ± 42.67 µg/kg) than at Ataba (123.53 ± 38.91 µg/kg). Naphthalene contributed 38.7–40.8% of the total measured burden, while phenanthrene contributed 32.3–36.5%. Ecological risk quotients ranged from 0.14 at ATB-3 to 0.39 at BOD-2, with all stations classified as low risk under the adopted risk framework. Conclusion: The sediments of the Ataba–Bodo estuary contained measurable concentrations of the five investigated LMW-PAHs, with a greater overall burden observed in Bodo than in Ataba. Naphthalene and phenanthrene were the principal contributors to the measured PAH burden. Although the calculated ecological risk remained low at all stations, the comparatively elevated concentrations and risk quotient at BOD-2 identify this location as a priority for continued environmental monitoring.