Polycyclic aromatic hydrocarbon levels and health risk assessment of sediment and shellfish from coastal communities in the Niger Delta, Nigeria

Abstract

This study investigated the occurrence, distribution, and potential health risks of polycyclic aromatic hydrocarbons (PAHs) in sediment and shellfish collected from the Santa Barbara River (Nembe) and Sangana River (Brass), two coastal communities in the Niger Delta, Nigeria. Sixteen US EPA priority PAHs were quantified using gas chromatography–mass spectrometry (GC–MS) following standardised extraction and clean-up procedures. Sediment PAH concentrations ranged from 0.14 to 0.18 mg/kg in the Sangana River and 0.28–0.43 mg/kg in the Santa Barbara River. PAH concentrations in all shellfish samples analysed from both study areas were below the analytical detection limits of the GC-MS method applied. Carcinogenic risk assessment for sediment indicated that risks to both adults and children were predominantly higher in the Santa Barbara River than in the Sangana River. Based on the PAH4 index, no quantifiable carcinogenic PAH burden was detected in shellfish under the conditions of this study. However, given that the shellfish results were uniformly below detection limits, rather than confirmed zero values, this establishes the non-detection of PAHs should be interpreted cautiously, as it most likely reflects concentrations below the analytical detection limits and low environmental bioavailability rather than the complete absence of contamination from shellfish consumption. This reflects the sensitivity threshold of the analytical method and the constraints of a limited sample size ( n = 4 sediment samples per site) collected at a single point in time. Temporal dynamics, seasonal variability, and species-specific accumulation patterns were not assessed and represent important uncertainties in the risk characterisation. These constraints notwithstanding, the data support the value of sustained, long-term PAH monitoring in Niger Delta coastal ecosystems, where ongoing petroleum activities pose a persistent contamination risk and where shellfish remain a critical dietary protein source for local communities.