The monitoring and risk assessment of aliphatic and aromatic hydrocarbons in sediments of the Red Sea, Egypt

Abstract

Polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbon were analyzed in sediments collected from the Suez Gulf, Aqaba Gulf and the Red Sea proper stations Egypt. A geological study demonstrated that the sediments in the studied area have a nature from very fine sand to very coarse sand, mainly biogenic fragments, and carbonate aggregates. Total aliphatic hydrocarbon concentrations (C14–C32) ranged from 33.97 to 553.48ng/g with a mean value of 174.8±167.06. The highest and lowest alkane concentrations are recorded at El-Tour and Ras Mohamed, respectively. Accordingly, the variation in n-alkanes content may refer to the anthropogenic sources (sewage, industrial discharges, and shipping activities) and natural inputs (submerged/floating macrophytes and emergent terrestrial plants and microbial activity). Meanwhile, ΣPAH concentrations were in the range of 0.74–456.91ng/g, with the mean value of 32.94ng/g. The highest concentration of total PAHs is recorded in sediments collected from El-Quseir (456.91ng/g), followed by that in Sharm El Mayaa (100.05ng/g) and Suez 10 (97.19ng/g); while lower concentrations are detected in Sheraton (0.74ng/g), Ras Mohamed and Na’ama Bay (0.74, 6.86 and 11.1ng/g, respectively). In this context, ratio of low molecular weight of PAHs (2- and 3-rings) to high (4- to 6-rings) has been used to differentiate between the pyrogenic and petrogenic sources of PAHs in the studied samples. In all studied stations, ΣLPAHs/ΣHPAHs ratios were <1, revealing their pyrogenic sources. The concentration levels of PAHs in the current study were compared to the effect range low (ERL) and the effect range medium (ERM) values; the average concentration of level of PAHs for all investigated stations was below the ERL except El-Quseir station which recorded PAHs higher than the ERL but still lower than the ERM. This finding indicated that PAHs in surface sediments of the studied area have no adverse biological effects except at El-Quseir which may cause mild adverse biological effects but not acute effects. To assess the potential health risk of PAHs; the BaP equivalent (BaPE) is used. High levels of BaPE values were found at El-Quseir only, indicating that PAHs in this site showed relatively high toxicity among all sites. Toxic equivalency factors (TEFs) of seven carcinogenic PAHs (BaA, BbF, BkF, BaP, Chr, DBA and InP), were used to quantitatively assess the potential toxicological significance to human health. In this study, the toxic equivalent (TEQcarc) values of sediment samples varied from not detected (ND) to 72.27ngTEQg−1, with the mean value of 2.94ngTEQg−1. The higher total TEQcarc values were found at El-Quseir Station 72.27ngTEQg−1.