Assessing ecological and health risks of PAH compounds in Anzali Wetland: A weight of evidence perspective

The Anzali Wetland, an internationally protected site under the Ramsar Convention, has experienced increasing concentrations of polycyclic aromatic hydrocarbons (PAHs) due to various anthropogenic activities, including transfer bridges that cross the wetland, military installations, commercial shipping, fishing boats, urban sewage systems, gas stations, and tourism. These PAH emissions pose significant health risks to the seafood-dependent local population, resulting in pollutant bioaccumulation and eventual entry into the human food chain. Despite the ecological importance of Anzali Wetland, comprehensive studies quantifying PAH exposure risks and their direct health implications remain scarce. To address this gap, this study provides a detailed assessment of PAH contamination levels and associated human health risks. To systematically evaluate these risks, PAH contamination in sediments and clam was examined across different wetland regions. The study focused on two distinct areas: the central-northern regions, characterized by high PAH emissions, and the southern region, where PAH concentrations were lower. The clam species Anodonta cygnea was used as a sentinel organism for evaluating health risks associated with PAHs. PAHs in sediment and clam soft tissue samples were extracted using a Soxhlet apparatus. The obtained extract was then analyzed to identify and quantify 30 PAH compounds found in these samples. Column chromatography and spectrometry were utilized for the analysis. We integrated ecological and health risk assessments using the weight of evidence (WOE) approach, combining two lines of evidence (LOE): chemical characterization (LOE1) and human health considerations (LOE3). A distinct hazard quotient was calculated for each LOE before being synthesized into a comprehensive WOE assessment. Chemical analysis (HQ_C) of sediments from the central and northern wetlands indicated a ‘Major’ chemical hazard, while the southern wetland showed ‘no risk’ across all sampling sites. The human health analysis (HQ_hh) of clams revealed an ‘Absent’ risk for PAHs. The WOE approach, applied for the first time in Anzali Wetland, yields a predominantly “Slight” risk rating, despite the presence of multiple severely polluted sites in the central/northern region, offering a valuable assessment of ecological conditions that can enhance conservation strategies.

Based on the highest contributors to PAH contamination from Asphalt, tire particles, and Gasoline leakage in Anzali wetland, replacing asphalt coatings on bridges and roads near the wetland with permeable pavement can reduce runoff pollution during rainfall, enforcing high-quality tire standards will help minimize rubber particle contamination, and relocating fuel stations and ship docking stations away from ecologically sensitive sites, along with traffic control measures can further prevent direct contamination and environmental impact.