Risk assessment and contaminant characterization of PCBs, PAHs, and heavy metals in Pichavaram mangrove sediments, Tamil Nadu, India

The coastal region of Pichavaram, Tamil Nadu, India, is a critical ecological zone that supports diverse marine life and local livelihoods; however, it faces significant environmental challenges due to contamination from persistent toxic substances (PTSs) and heavy metals, which pose serious ecological and human health risks. In the present study, sediment samples collected from the mangrove environment were tested for polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and heavy metals. The results revealed elevated concentrations of & sum;PCBs (6-124 ng/g) and & sum;PAHs (3.19-37.8 ng/g), alongside heavy metals such as Pb (11-26 mu g/g), Cd (0.3-0.87 mu g/g), Cu (below detectable levels, bdl)-31 mu g/g), Ni (bdl-119 mu g/g), and Zn (27-109 mu g/g), indicating significant environmental contamination. The total PCB concentrations surpassed the guideline values, indicating potential risks to aquatic life. Elevated naphthalene levels in Kodipallam suggest petrogenic inputs from oil spills and urban runoff. Carcinogenic PAHs, including benzo[a]pyrene, are found at high levels in industrial zones such as Killai, and pose moderate ecological risks. Heavy metals such as As (68-140 mu g/g), Cr (25-120 mu g/g), and Mn (94-471 mu g/g) often exceeded the threshold effect levels (TEL) and probable effect levels (PEL), indicating significant ecological risks and potential human health impacts. Coastal sediment contamination, driven by discharges from chemical industries, oil refineries, metal manufacturing, and agricultural runoff, poses long-term risks to marine life and human health through the bioaccumulation of persistent pollutants in the food chain. This study provides crucial baseline data for future monitoring and emphasizes the need for stricter regulatory measures and pollution management strategies. Recommendations include regular sediment quality monitoring, public awareness campaigns on pollution sources, and sustainable practices to mitigate risks, thereby protecting the coastal environment and local communities.