Risk assessment of polycyclic aromatic hydrocarbons (PAHs) in River Nile up- and downstream of a densely populated area.

A biomonitoring study was conducted to evaluate levels of eleven polycyclic aromatic hydrocarbons (PAHs) in water, sediment and wild Nile tilapia (Oreochromis niloticus) samples collected up- and downstream of Cairo sector of the River Nile, Egypt. The scaled mass index (SMI), as a fish body mass-length relationship, performed better in indicating the ecosystem and fish conditions. The total PAHs in water samples had a range of 0.0156-0.0269 mg/L, while that in sediment samples ranged from 0.723 to 1.078 mg/kg dry weight and that in fish muscles ranged from 4.065 to 10.033 mg/kg wet weight. Pollutant source appraisal was determined by diagnostic ratios and proved the predominance of pyrogenic sources in water, petrogenic sources in fish, and mixed source origin in sediment. Human health risks associated with fish consumption showed that non-cancer adverse health effects are not expected to occur but the calculated lifetime cancer risk (LCR) for the total PAHs proved that the fish muscles are not safe for human consumption at both sites. Regular monitoring programs and mitigation efforts should be considered in the near future along such areas heavily influenced by human activities.