Risk Assessment and Source Identification of Some Persistent Organic Pollutants In Water, Sediment, and Clarias Gariepinus From Okrika Axis of Bonny River

Persistent organic pollutants (POPs) have been of great concern because of their toxic natures. This study investigated selected POPs in surface water, sediment and Clarias gariepinus (African Sharptooth Catfish) from four sampling locations along the Okrika axis of Bonny River, Rivers State, Nigeria. Water and sediment samples were collected from representative stations and fish were obtained from local fishermen. Six POP congeners (BDE-47, BDE-99, BDE-209, PCB-28, PCB-118 and PCB-153) were quantified. POPs in water ranged from 0.32 ± 0.02 to 4.73 ±  0.23, in sediment from 2.7 ± 0.1 to 76.5 ± 3.9, and in Clarias gariepinus from 3.9 ±0.20 to 54.4 ±  2.60. Accumulation data was assessed by bioaccumulation factor (BAF) and biota–sediment accumulation factor (BSAF); and human/ecological risk was estimated via estimated daily intake (EDI), hazard quotient (HQ) and hazard index (HI). Results showed widespread contamination of the Bonny River by POPs. Heavy burden of sediment-associated POPs (especially BDE-209) and biota-associated lighter congeners (BDE-47 and PCB-28) The BAF and BSAF metrics also showed that the lower-molecular weight PBDEs and light PCBs strongly partition into fish tissue while the heavier congeners are more sediment-bound. Most risk screening determined some exceedances of some of these internationally recognized guidance (WHO, US EPA and, EU environmental quality standards) for some contaminants, and the many individual HQs and cumulative HIs greater than unity in turn indicated the potential for non-carcinogenic risk from chronic exposure via water ingestion and fish consumption. Collectively, the data indicated that Bonny River is chemically stressed by mixed inputs from oil-related activities, industrial effluents and domestic discharges. The concurrence of elevated contamination indices, strong bioaccumulation and HI exceedances highlights an urgent need for monitoring, targeted source control, regulatory enforcement and remediation to protect aquatic ecosystems and public health in the Niger Delta.