Distribution and bioavailability of polycyclic aromatic hydrocarbons in oyster (Saccostrea cucullate) and periwinkle (Littorina littorea) from sediment in the Sombreiro River Estuary, Niger Delta, Nigeria

Abstract

In recent time, the ubiquitous, persistent and the toxicities characteristics of polycyclic aromatic hydrocarbons (PAHs) in estuarine ecosystems have generated serious concerns globally. In this study, the bioavailability and distribution of PAHs in sediments, oysters and periwinkles from the Sombreiro river estuary in the Niger Delta, Nigeria was investigated. The levels of the ∑16 PAHs in the sediment, oyster and periwinkle ranged from 495 to 12811 µg/kg, 200 to 32469 µg/kg and 2623 to 20293 µg/kg respectively. The results revealed that the sediments, oysters and periwinkles from the Sombreiro estuary were heavily contaminated with PAHs and the 3- and 4-rings being the dominant PAHs. Linear regression analysis showed that there was significant positive relationship between these matrices. Bioavailability assessment using BSAF indicated that the BSAF of ∑16 PAHs (mean BSAF = 2.38 for oyster and 3.81 for periwinkle) and that of individual PAHs except BkF, BaP, IndP and BghiP for oyster and BbF and BkF for periwinkles were > 1 and indicated that PAHs bioaccumulated in the oyster tissues. The 3- and 4- rings PAHs were more available to the oyster and periwinkle indicating greater risk of these PAHs. There was no correlation between BSAF and log K_ow which may be due to fresh and continuous inputs of PAHs and sampling period. The source apportionment of PAHs revealed that the PAHs were from both pyrogenic and petrogenic sources with significant contribution from pyrogenic inputs. The health risks assessed based on the actual PAHs concentrations and BSAF indicated that there was adverse non-carcinogenic risk from human exposure to the PAHs in the sediments but not from oysters and periwinkles. However, there were potential toxic, mutagenic and carcinogenic effects to humans exposed to PAHs in sediments, oysters and periwinkles from the Sombreiro estuary. In the overall, the health risk level in children were higher than the values reported for adults. The risks assessed based on actual PAHs concentrations were 34 to 389 times (for oyster) and 16 to 382 times (for periwinkle) higher than those based on BSAF. This implies that using the actual PAHs concentration in risk assessment will over overestimate the risk as most of the actual concentration is not bioavailable.