Environmental Assessment of Refinery-Derived Hydrocarbon and Trace Metal Contamination in Coastal and Groundwater Systems: A Case Study from Zawia, Libya

Oil refining activities can represent a persistent source of hydrocarbon contamination in coastal and groundwater environments, particularly in regions where long-term monitoring data are limited. This study presents an integrated environmental assessment of refinery-derived hydrocarbon and trace metal contamination in offshore, shoreline, and groundwater systems surrounding the Zawia Refinery, western Libya. Twenty samples were collected from offshore waters, shoreline zones, and groundwater wells and analysed for total petroleum hydrocarbons (TPH), chemical oxygen demand (COD), dissolved oxygen (DO), total dissolved solids (TDS), pH, and selected trace metals. The results show strong spatial variability in contamination, with offshore stations AS7 and AS8 exhibiting the highest TPH concentrations (up to 43 mg/L). Groundwater wells AG2 and AG6 also showed elevated TPH, accompanied by pronounced oxygen depletion, indicating strongly reducing conditions in the most impacted wells. Correlation analysis identified a strong positive relationship between TPH and COD and a significant negative relationship between TPH and DO, consistent with oxygen consumption during microbial degradation of petroleum hydrocarbons. Nickel and vanadium enrichment in the most contaminated groundwater wells further supports refinery-related source signatures. Overall, the findings indicate both horizontal dispersion in marine waters and vertical migration into the shallow aquifer, emphasizing the need for integrated monitoring and targeted mitigation in refinery-impacted Mediterranean coastal settings.