Diagnostic Ratios and Ecological Risk of Non-carcinogenic Polycyclic Aromatic Hydrocarbons (ncPAHs) in Egi Crude Oil Communities, Nigeria

The loadings of PAHs, its diagnostic ratios and ncPAHs at three cluster communities in Egi sub district of Niger-Delta with geographic coordinates of latitude 150 32ʹ 50ʺ N and longitude 60 34ʹ 42ʺ E were ascertained using Gas Chromatography (GC-FID, HP 5890 Series). The diagnostic ratios showed that Obagi had an LMW/HMW ratio of 0.2340, Ibewa's was 0.2222, and Obite's was 0.2549. In Obagi, the proportion of Low Molecular Weight (LMW) PAHs compared to High Molecular Weight (HMW) PAHs was 19%, while in Obite it was 18%, and in the Ibewa cluster it was 20%. The sediments of the Obagi, Obite, and Ibewa cluster sites exhibited a significant abundance of PAHs derived from pyrogenic sources, as evidenced by the presence of LMW/HWM ratios below 1. The identified ncPAHs include: Naphthalene, Acenaphthene, Acenaphthylene, Fluorene, Anthracene, Phenanthrene, Fluoranthene, Pyrene and Benzo(ghi)perylene. According to the results obtained the Obite cluster area exhibited the lowest concentrations (1.503mg/Kg) amongst the ncPAHs, while the Obagi study zone demonstrated the highest concentrations (1.5733mg/Kg). Among the nc(PAHs) examined, benzo (g,h,i) perylene exhibited the highest concentrations (2.086mg/Kg) across all locations, whereas acenaphthylene displayed the lowest concentration (0.123mg/kg) across the three cluster areas. However, none of the three study locations had any ncPAHs that are above the maximum permissible limit. Results from the application of risk quotient models (RQNCs and RQMPCs) to assess the ecological risk of ncPAHs as presented indicated that all the sites where these rivers' sediments were tested had RQNCs values for specific ncPAHs below 1, implying that these ncPAHs pose little or no danger to ecosystems. Also, the RQMPC score is less than 1, it means that the contamination from individual ncPAHs chemicals do not necessitate immediate remediation. Because the RQNCs and RQMPCs for a single PAH molecule are both less than 1, the contamination it generates might be considered low risk. Thus, few measures of control or correction would be required. The ecological risk of non-carcinogenic PAHs using RQMPCs and RQNCs indicated a very negligible risk which could be due to factors like heavy flooding that washed away soil surfaces. Application of Detoxification by chemical reaction technology should be used as future remediation method if there is need.