Abstract The Gafsa-Metlaoui basin is responsible for over 90% of Tunisia’s phosphate production. It yields considerable sludge waste enriched with potentially toxic elements (Zn, Cr, Cu, Ni, and Cd). Despite well-documented total metal concentrations, insights into their precise geochemical fractionation and environmental mobility under arid conditions are notably lacking. In this study of the speciation, mobility, and ecological risk of these potentially toxic elements (PTEs), the Tessier sequential extraction procedure was applied to sludge samples from the region’s drainage network. Critically, this investigation presents the first comprehensive Tessier-based assessment of Metlaoui phosphate sludge and, uniquely, directly links PTE speciation to site-specific acidification processes induced by phosphogypsum leachates, a causal relationship previously overlooked. The selected sampling sites span major drainage sectors with differentiated industrial input signatures, ensuring robust spatial representation. Results indicated that although PTEs are predominantly associated with the stable residual fraction (44%), a substantial proportion (56%) is bound to more labile phases (exchangeable, carbonate, Fe/Mn oxides, and organic matter). Critically, the risk assessment code (RAC) identified Cd (43%) as posing a high risk and Ni (29%) a moderate risk due to their association with the most bioavailable fractions. The mobility index (MI) confirmed that Ni (50%) and Cd (45%) are highly mobile and susceptible to leaching. A key novelty of this research lies in the explicit demonstration, via principal component analysis (PCA), that pH is the master variable dictating PTE speciation. The strong negative correlations observed suggest that acidification (the acidity of phosphogypsum leachates) could significantly promote increased metal mobilization, a factor traditionally recognized as a source of contamination but which has never previously been quantified as the primary factor influencing the in situ mobility of PTE within the Metlaoui phosphate sludge deposits. By linking solid-phase speciation to site-specific geochemical triggers (e.g., acidification and redox changes), this study moves beyond total concentration surveys to provide a process-based risk assessment. The findings underscore the urgent need for engineered sludge management strategies, such as alkaline stabilization or phytoremediation, to mitigate the imminent threats to groundwater and ecosystem health in this vulnerable region, where shallow water tables and seasonal flooding create favorable conditions for contaminant transport.
Abstract This study systematically characterized volatile organic compound (VOC) compositions across cuisines in China, examined how edible oils affect VOC/polycyclic aromatic hydrocarbon (PAH) emissions, and evaluated associated health risks using both deterministic and Monte Carlo probabilistic models, from which a tiered health-risk early-warning classification was derived. Results showed distinct cuisine-specific VOC profiles: high-temperature frying cuisines [barbecue (BB) and western fast food (KFC)] were dominated by alkanes, whereas cooking-wine cuisines [Hunan cuisine (XC) and western cuisine (WC)] had high alcohols (13.2%–29.2% ethanol); Sichuan cuisine (CC) showed high VOC compositional similarity with the other cuisines ( similarity > 0.6 ). Rapeseed oil emitted the most particulate matter, soybean oil emitted the most nonmethane hydrocarbons, and both produced the highest PAHs, notably anthracene ( 276.88 μg m − 3 ) and benzo[a]pyrene. Noncarcinogenic risk arose mainly from acrolein, and the lifetime carcinogenic risk (LCR) exceeded 1.0 × 10 − 6 for all cuisines. VOCs contributed 86.3%–94.1% of total cancer risk and PAHs 5.9%–13.7%, the latter dominated by benzo[a]pyrene. Applying the proposed five-level early-warning scheme, high-oil, high-temperature methods (barbecue and Sichuan cuisine) reached the highest warning levels, and occupational workers were consistently classified one to two levels above nearby residents. The results highlight the need for targeted control of key pollutants (e.g., acrolein and 1,3-butadiene, benzo[a]pyrene) and for occupational protection in catering kitchens.
Abstract During voluntary and involuntary spill events, total dissolved gas (TDG) levels may increase, potentially causing gas bubble disease (GBD) in fish. At hydropower plants (HPPs), one approach to mitigate TDG supersaturation is the use of deflectors in spillway design. Ideally, deflector design integrates physical modeling with mathematical or computational approaches; however, such simulations typically require substantial computational resources. This study presents a cellular automata model to estimate TDG levels using hydrodynamic velocity fields simulated in OpenFOAM as input data. The main advantage of this approach is its low computational cost because it can be executed on a personal computer, making it suitable for preliminary studies. In contrast, the simulations conducted for the design of the Colíder HPP spillway deflector required high-performance computing resources, utilizing a cluster with 96 processors.
In recent decades, intensified industrial and agricultural activities have caused widespread and ongoing metal(loid) contamination in soils, creating serious environmental and health risks worldwide. This study assesses the combined interactions and effects of natural organic matter [humic acid (HA) at 0.4% by weight/weight] and iron oxides [goethite nanorods (GN) at 1% by weight/weight] on the leachability of arsenate [As(V)] and chromate [Cr(VI)] in soil under two scenarios. In the predosing scenario, soil containing GN and/or HA was packed into a column and treated with solutions of Cr(VI), As(V), or both (each at 20 mg L-1) at a flow rate of 0.5 mL min-1. In the postdosing scenario, the soil was spiked with As(V), Cr(VI), or both, then mixed with GN and/or HA and incubated for 24 h, and packed into columns. Then, both the soil columns were leached with a 0.01-M CaCl2 solution. The effluent analyses showed that in the predosing scenario, HA was effective in adsorbing/reducing Cr(VI), achieving decrements of 36% and 90% in the absence and presence of As, respectively. GN decreased As leachability by approximately 70%, though its efficiency decreased in the presence of Cr(VI). Conversely, HA increased As leachability, particularly in the presence of Cr(VI). Similar outcomes were observed in the post-dosing scenario. Compared to the predosing scenario, the post-dosing scenario showed improved performance regarding Cr(VI) and As(V) adsorption and retention. The findings underscore the significant impact of coexisting oxyanions on the leachability of contaminants in soil, particularly when iron oxides and organic matter are present. These factors should be carefully considered before applying any treatment that relies on redox or adsorption processes, highlighting the complex interactions in soil remediation strategies.
