Introduction: Coastal sediment contamination by petroleum hydrocarbons and heavy metals is one of the most significant environmental concerns in industrial areas. Due to their persistence, toxicity, and ability to accumulate in sediments and transfer to the food chain, these pollutants have long-term effects on marine ecosystems. Surface sediments are both a reservoir for pollutants and can act as a secondary source under certain conditions. Shahid Salimi Neka Power Plant in Mazandaran Province uses Caspian Sea water for cooling and discharges its effluent through specific channels. The aim of this study was to evaluate the concentrations of Total Petroleum Hydrocarbons (TPHs), including Total Petroleum Hydrocarbon-Gasoline Range Organics (TPH-GRO), Total Petroleum Hydrocarbon-Diesel Range Organics (TPH-DRO), and Total Petroleum Hydrocarbons–Crude Oil Range Organics (TPH-CRO), as well as eight heavy metals (cadmium, lead, zinc, copper, nickel, mercury, iron, and manganese) in surface sediments around the power plant to determine the possible role of the effluent in increasing contamination.
Materials and Methods: The study was conducted in the coastal area adjacent to Shahid Salimi Neka Power Plant, where three sampling stations were selected. Station 1 was located northeast of the first wastewater outlet, Station 2 was situated between the first and second outlets, and Station 3 served as a control station outside the area of direct influence. Surface sediment samples were collected in May, June, and July 2021 using a Van Veen grab sampler (20 × 25 cm). For petroleum hydrocarbon analysis, the samples were freeze-dried and extracted using a mixture of n-hexane and dichloromethane in a Soxhlet apparatus. TPH-GRO, TPH-DRO and TPH-CRO were determined in milligrams per kilogram of dry weight (mg/kg dw). Heavy metal concentrations were also determined using atomic absorption spectrometry (AAS) following acid digestion of the sediment samples.
Results: The results revealed considerable spatial and temporal variations in petroleum hydrocarbon concentrations among the sampling stations and across the sampling months. The highest petroleum hydrocarbon concentrations were recorded at Station 1 in May and July and at Station 2 in June, whereas the control station generally exhibited lower concentrations. Among the investigated metals, zinc and manganese showed relatively high concentrations. Zinc concentrations at the stations adjacent to the wastewater outlets exceeded the Canadian Interim Sediment Quality Guidelines (ISQG), potentially indicating contamination pressure in this area. Relatively high concentrations of certain metals, including copper, nickel, and lead, were also observed in some samples. However, no consistent increasing trend in metal concentrations was evident with decreasing distance from the wastewater outlets.
Discussion: The findings indicate that coastal sediments adjacent to the power plant are subject to varying degrees of contamination by petroleum hydrocarbons and certain heavy metals. Nevertheless, differences in contaminant distribution among sampling months and stations suggest that the observed variations cannot be attributed solely to wastewater discharge from the power plant. Factors such as the physical and chemical properties of sediments, hydrodynamic conditions, particle transport and deposition, and pollutant inputs from other coastal sources may also influence contaminant distribution. Therefore, regular long-term monitoring, investigation of sediment characteristics and organic matter content, and comparison of measured concentrations with established marine environmental quality standards are necessary to provide a more comprehensive assessment of contamination and determine the potential contributions of different pollution sources.