Heavy metal sources and associated ecological and human health risks in coastal islands of the Ganges–Brahmaputra–Meghna delta, Bangladesh

The coastal islands of the Ganges–Brahmaputra–Meghna delta are ecologically vital but increasingly threatened by rising heavy metal contamination from natural and anthropogenic sources. This study assessed ten metals (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sn, and Zn) in surface sediments collected from thirteen southern coastal islands using ICP–MS. Results revealed pronounced spatial heterogeneity, with major contamination hotspots at Salimpur, Urir Char, and Kutubdia. Cadmium and arsenic exhibited the highest enrichment, exceeding upper continental crust values by 18.4 and 2.3 times, respectively. Pollution load index (PLI) values greater than one indicated a substantial decline in sediment quality. The potential ecological risk index (PERI) revealed moderate to very high ecological risk dominated by Cd, while the toxic risk index (TRI) suggested low to moderate toxic risk. Although non-carcinogenic risks were negligible, cumulative carcinogenic risks from Cr, Ni, Cd, and As exceeded the USEPA safety threshold. Positive Matrix Factorization (PMF) and Principal Component Analysis–Multiple Linear Regression (PCA–MLR) indicated that metals originated from geogenic and anthropogenic sources, mainly associated with shipbreaking, agriculture, and groundwater extraction. These findings provide essential baseline data to inform targeted mitigation and regulatory measures for the sustainable management of the GBM delta. • First multi-island assessment of heavy metals in GBM delta sediments. • Cd and As showed highest enrichment, exceeding upper continental crust values. • Pollution load index revealed major decline in sediment quality at key sites. • Carcinogenic risk from Cr, Ni, Cd, and As exceeded USEPA safety threshold. • PMF and PCA–MLR identified shipbreaking, geogenic, agriculture, and groundwater sources.