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

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 0.41–4.75; median 1.09) with low ecological risk (RI < 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.