Bioaccumulation of Polycyclic Aromatic Hydrocarbons in Sediments and Bivalves of Bonny Estuary, Rivers State, South South Nigeria

Polycyclic aromatic hydrocarbons are persistent organic pollutants produced by incomplete combustion of petroleum and organic matter, and they accumulate in estuarine sediments and filter-feeding organisms, posing ecological and human health risks. This study quantified polycyclic aromatic hydrocarbon concentrations in sediments and in the bivalve Crassostrea gasar collected from six sites in Bonny Estuary, Rivers State. Samples were collected seasonally over one year and analysed using gas chromatography-mass spectrometry. Biota-sediment accumulation factors were calculated to assess bioaccumulation efficiency. Human health risk from bivalve consumption was estimated using carcinogenic and non-carcinogenic risk quotients based on estimated daily intake by local consumers. Sediment quality guideline comparisons were applied for ecological risk assessment. Results showed total polycyclic aromatic hydrocarbon concentrations in sediments ranging from 340 to 8,640 nanograms per gram dry weight, with highest concentrations near oil terminal berths. Bivalve polycyclic aromatic hydrocarbon concentrations were significantly correlated with sediment concentrations. High molecular weight compounds with high carcinogenic potency dominated the bivalve tissue burden. Carcinogenic risk quotients for regular bivalve consumers exceeded the United States Environmental Protection Agency acceptable risk threshold at four of six sites. The study demonstrates significant polycyclic aromatic hydrocarbon contamination and associated health risks in Bonny Estuary and recommends inclusion of bivalve contaminant monitoring in routine National Oil Spill Detection and Response Agency environmental assessment protocols. Keywords: polycyclic aromatic hydrocarbons, bioaccumulation, Bonny Estuary, bivalves, Rivers State.