"Bentogypsum", a phosphoric acid purification residue: Characterization and implications for environmental and human health risk in Gabes (SE Tunisia).
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The present study provides a comprehensive physico-chemical characterization and an integrated screening-level assessment of environmental and human health risks associated with "bentogypsum" (BG), a phosphoric acid purification residue generated by the phosphate fertilizer industry in Gabes (SE Tunisia) and stocked in open-air stockpiles. BG is identified as a fine-grained, low-density, and highly acidic solid waste dominated by calcium phosphate minerals (gypsum, bassanite, and anhydrite), with additional fluoride-bearing phases and a complex microstructure. Geochemical analyses reveal elevated concentrations of potentially toxic metal/metalloid elements, notably cadmium, arsenic, lead, chromium and uranium. On-site environmental risk assessment consistently indicates extremely high levels of contamination, largely exceeding commonly accepted screening thresholds. On-site human health risk assessment further highlights significant non-carcinogenic and carcinogenic risks for population living nearby the BG stockpiles, with children identified as the most vulnerable group. Oral ingestion is the dominant exposure pathway, and cadmium represents the main contributor to both, non-cancer and cancer risks. Taken together, these results demonstrate that BG cannot be considered an inert industrial by-product and should be classified as a hazardous waste. Further, the current open-air storage conditions on degraded containment infrastructures constitutes a major source of ongoing environmental dispersion and human exposure. This study emphasizes the urgent need for improved management, containment, and treatment strategies for bentogypsum, while providing a scientific basis for risk-based decision-making and future investigations at similar industrial sites worldwide.