Soil-to-shoot transfer of potentially toxic elements in a halophyte exposed to phosphate fertilizer industry...

Soil contamination by potentially toxic elements (PTEs) from phosphate fertilizer industry effluents (PFIE) is a persistent problem in arid regions, where industrial discharge often overlaps with natural halophytic vegetation and grazing activities. In this field-based study, we investigated the halophyte Sarcocornia fruticosa along a contamination gradient in southwestern Tunisia. We simultaneously examined soil PTE bioavailability, plant accumulation and translocation, physiological and metabolomic responses, and associated ecological and human health risks. Soils receiving PFIE showed elevated PTE concentrations, with Cd, As, Cr, and Ni reaching 2.6, 5.7, 30.3, and 12 mg kg^-1, respectively. Additionally, high phytoavailable fractions of Cd, As, Cr, Ni and Pb were measured in these soils reaching 1.25, 2, 33, 17.6 and 1.5 mg kg^-1, respectively. Despite increasing distance from the effluent source, PTE translocation to aerial parts remained substantial, with translocation factors up to 12 for Cr and 8 for Ni, highlighting sustained metal(loid) mobility within the soil-plant system. Correlation analyses indicated that PTE translocation was associated with contrasting soil controls, with salinity restricting shoot transfer for most elements and soil organic matter primarily influencing Cd mobility. Increasing PTE translocation coincided with a shift from adaptive antioxidant responses to a metabolically constrained stress-tolerance strategy along the contamination gradient. Critically, this apparent physiological tolerance did not correspond to reduced environmental risk. Ecological risk assessment indicated elevated risks for grazing animals (RQ > 1), while conservative human exposure scenarios revealed non-carcinogenic hazards (HQ > 1) for Cr and carcinogenic risks for Cd, Cr, and As exceeding acceptable thresholds (CR > 10^-4). Collectively, these site-specific observations indicate that physiological tolerance in S. fruticosa does not necessarily correspond to reduced ecological or human health risks. This study highlights the value of integrating soil bioavailability, plant functional responses, and risk assessment for improving the evaluation and monitoring of industrially impacted dryland ecosystems.