Coal Tar Toxicity in the Mangrove Clam Polymesoda erosa

This study provides the first evidence that coal tar, one of the most concentrated and chemically complex sources of PAHs, inflicts serious, dose-dependent damage on the mangrove clam Polymesoda erosa. Within just 28 days of exposure, coal tar drove progressive necrosis and structural collapse in gill and mantle tissue, disrupted energy reserves and protein metabolism, forced antioxidant systems into overdrive, destabilised ion regulation, and suppressed the animal's very ability to breathe and excrete waste normally. That a single pollutant can compromise an organism at every level from cell to tissue to whole-body physiology within such a short exposure window highlights how little resilience these bivalves have against sustained coal tar contamination. P. erosa is a keystone filter-feeder and a food source that coastal communities such as those in Chorao, Tiswadi, Goa, depend on directly. Continued or expanding coal tar contamination of these habitats, whether from legacy manufactured-gas-plant residues or ongoing sources such as coal-tar-based sealants and paints, places bivalve populations, estuarine food webs, and ultimately human health and livelihoods on a trajectory toward silent, cumulative harm. The absence of prior toxicological data on coal tar in this species is itself a warning: a widely consumed, ecologically vital organism has been at risk without documentation until now. Future work should extend this exposure period to assess whether these effects intensify, plateau, or become irreversible over longer timescales, and should quantify tissue-level PAH bioaccumulation and depuration kinetics directly. Molecular investigations into oxidative stress and apoptotic pathways, alongside reproductive and developmental endpoints, would clarify whether coal tar threatens not just individual health but population persistence. Parallel human health risk assessments, evaluating PAH transfer through consumption of contaminated bivalves, are urgently needed to translate these findings into actionable guidance for coastal communities and regulatory bodies alike.

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