Hidden contaminants in a coral paradise: fate, transport, source apportionment, and toxicity of polycyclic aromatic hydrocarbons in the coral reef ecosystems of the Lakshadweep archipelago.

This study examined the environmental fate, source apportionment, and associated ecological and human health risks of polycyclic aromatic hydrocarbons (PAHs) in the coral reef ecosystems of four inhabited islands in the Lakshadweep Archipelago (Kadmat, Kiltan, Kalpeni, and Minicoy). Water, suspended particulate matter (SPM), and sediments were collected from reef lagoons during April 2025 and analysed for 16 PAHs congeners designated as priority by the United States Environmental Protection Agency (USEPA). PAHs were in the range of 20.9-240 ng/L in the dissolved phase, 146-356 ng/L in the SPM, and 2.05-22.2 ng/g in sediments. PAH transport and sedimentary accumulation differ markedly from those in siliciclastic coastal environments due to the dominance of carbonate-rich, organic-matter-deficient, highly permeable sediments and strong hydrodynamics that promote rapid particle export to adjacent offshore waters. As a result, reef lagoons act as dynamic conduits that promote contaminant exchange with the Arabian Sea, thereby limiting long-term contaminant accumulation in the lagoon sediments. Source apportionment studies indicated mixed petrogenic and pyrogenic PAHs sources, primarily associated with navigational activities, fuel handling, diesel-powered energy generation, and combustion-related activities. Ecological risk assessment indicated negligible risks from sedimentary PAHs, while dissolved and SPM-bound PAHs posed low to moderate ecological risks. Incremental lifetime cancer risk (ILCR) values for all age groups were within the potential low-risk category, with dermal contact identified as the dominant exposure pathway. This study provides critical baseline information on transport behaviour and ecological implications of PAHs in the coral reef ecosystems of Lakshadweep and recommends sustained environmental monitoring and targeted management strategies to protect the ecological integrity of these coral reef systems under mounting anthropogenic perturbations.