Distribution and risk assessment of phenols and polycyclic aromatic hydrocarbons in sediments from the continental shelf adjacent to Nile River estuaries, Egypt

Background

The highly industrialized areas characterize the delta coasts of the world, due to the discharging of large quantity of wastewater into the river estuaries. The entrance of phenolic compounds and PAHs into the aquatic environment has not been sufficiently studied on the Egyptian Mediterranean coast. The article examines the content and ecological risks associated with 11 phenolic compounds and 14 PAHs in the bottom sediments of the Nile River estuaries, the largest river systems that discharged into the Mediterranean Sea.

Results

Phenolic and PAHs compounds concentrations were determined by high-performance liquid chromatography (HPLC) and GC MS (Hewlett-Packard 5889B MS ‘Engine’) respectively. The total concentration of 11 phenolic compounds (∑PC11) in sediment ranged from undetected to 272.48 μg/g with an average of 7.95 μg/g. For individual phenolic compound, the mean concentration of 4-nitrophenol was the highest in sediment (33.32 μg/g). The total concentration of nonchlorophenols (∑NCP6) was significantly higher than that of 5 chlorophenols (∑CP5) in all areas. The concentrations of total PAHs ranged between 12,198 to 26,551 ng/g, with an average of 22,009 ng/g. PAH levels have increased in the two estuaries under the influence of riverine inputs from the Nile River. LMW are clearly predominant over HMW (ratio is between 0.7 and 1.18) in the most sediment. The LMW/HMW ratio ranged between 0.23 and 0.39, indicating both pyrolytic and petrogenic sources. The total concentration of potentially carcinogenic PAHs (∑PAH7) ranged from 5049 to 15,144 ng/g. The rest individuals including Acy, Ace, Phe, Flu, BaA, BaP and DahA were (≥ERM) suggesting frequently harmful biological impairments.

Conclusions

The highest concentrations of phenols and PAHs in the surface sediment occurred in the lower reach of the drainage outlets and land-based sources, suggesting that these pollutants accumulated along with runoffs from the input of the pollutants into the aquatic environment. The risk quotient reveals high ecological risks of the total phenolic and PAHs compounds in sediment. Thus, it is imperative to control the discharge of wastewater into the river so as to reduce the potential risks from phenols off Nile Delta sediments to the marine environment and consequently to humans.