Harmonised assessment of heavy-metal contamination and ecological risk in Vietnamese coastal and estuarine sediments: a verified multi-site synthesis

<jats:p>Assessments of potentially toxic elements (PTEs) in Vietnamese coastal and estuarine sediments are numerous but use heterogeneous geochemical baselines, normalisers and thresholds, preventing direct comparison. We compiled 18 source-verified sediment datasets spanning northern, central and southern Vietnam and five hydro-geomorphic settings, harmonised all concentrations to a common average-shale background, and recomputed a consistent index suite (contamination factor, geoaccumulation index, pollution load index PLI, potential ecological-risk index RI) benchmarked against CCME sediment-quality guidelines. Most sites are unpolluted to moderately contaminated (PLI 0.41&amp;ndash;4.75; median 1.09) with low ecological risk (RI &lt; 150 at 15 of 18 sites). Three hotspots stand out: the wastewater-fed Nhue River (Hanoi; PLI 4.75, RI 551), Ha Coi Bay (RI 482) and the Cam Estuary (PLI 2.19), driven by Cd, As, Pb and Cr. Cadmium and arsenic dominate the ecological-risk index. Contamination did not differ significantly among the three well-sampled settings (Kruskal-Wallis H = 1.97, p = 0.37): the contamination signal is dominated by local anthropogenic inputs rather than regional background differences. Principal component analysis (PC1 + PC2 = 92%) resolves a mixed lithogenic-anthropogenic association (Cr-Cu-Zn-As) and a separate Cd-Pb signal. We provide the harmonisation framework, verified dataset, and open computation pipeline to support standardised national monitoring.</jats:p>