Comparative Assessment of Heavy Metal Contamination and Pollution Trends in Indian Estuarine Sediments: Insights from East and West Coasts of India

This study presents a comparative assessment of heavy metal contamination in sediments from major Indian estuaries in recent decades. Metal concentration data were compiled from published literature and analyzed for Pb, Cd, Cr, Hg, As, Cu, Ni, Zn, Al, Fe, and Mn using indices such as effects range low-effect range median (ERL-ERM), contamination factor (CF), and pollution load index (PLI). Nickel frequently exceeded ERM thresholds (in 20 out of 62 studies), while Cd pollution was most severe (mean CF: 38.89), especially in the Godavari estuary (CF: 49.39–256.12), likely due to industrial discharge. Notably, the PLI of the Narmada estuary declined from 2.54 (2010) to 0.69 (2020), indicating improved effluent management. Two new metrics, temporal averaged PLI (TAPLI) and PLI rate (PLIR), were introduced to evaluate trends. The highest TAPLI values were in the Godavari (3.30) and Ulhas (3.81) estuaries. Negative PLIR values were seen in Uppanar, Zuari, Mahanadi, Mandovi, and Narmada, while Cauvery showed a positive value (0.35 PLI/year), with PLI increasing from 0.39 (2008) to 6.76 (2023). East (2.15) and west (2.24) coasts had a similar mean PLI value. These findings highlight the need for targeted estuarine remediation efforts.