Basin-scale multi-index assessment of heavy metal contamination and risk partitioning across intertidal-supratidal sands in an industrialized Mediterranean coast (Gulf of Gabès; Tunisia)

Abstract

Coastal sands in industrialized environments act as dynamic reservoirs of contaminants, yet their large-scale behavior and associated risks remain poorly constrained. This study presents a basin-scale assessment of heavy metals (Fe, Zn, Pb, Cd, and Cu) in intertidal and supratidal sands along a ∼ 60 km coastal transect (Kettana-Skhira, Gulf of Gabès), based on 40 surface sediment samples and multiple contamination and risk indices, such as enrichment factor (EF), geoaccumulation index (Igeo) and mean-ERM-Quotient (m-ERM-Q), and human health risk models. Elevated metal burdens were dominated by Pb > Cu > Zn > Cd, with Fe reaching up to ∼9.3 g/kg. Severe to very severe enrichment was observed for Cd and Pb (EF > 10), while Zn showed weak enrichment and Cu moderate enrichment. Igeo values indicate strong to extreme pollution for Cd (>3) and moderate to strong pollution for Pb (≈2–4). Spatially, the intertidal zone enhances Cd and Zn accumulation, whereas the supratidal zone preferentially traps atmospheric Pb and Cu deposition. Ecological assessment (m-ERM-Q up to 0.6) suggests moderate toxicity risk, while health risk results indicate negligible non-carcinogenic effects (HQ, HI) but notable carcinogenic risk (TCR: 10−4–10−3), affecting all sites for children and ∼ 45% of adults. Overall, the findings reveal strong anthropogenic contamination driven by phosphate-processing activities and atmospheric inputs, highlighting the need for targeted coastal pollution management. © 2026 Elsevier Ltd.