Characterization of the role of phosphogypsum foam in the transport of metals and radionuclides in the Southern Mediterranean Sea

Utilization of phosphogypsum and red mud in alfalfa cultivation

In this work, the utilization of phosphogypsum (PG), a waste coming from the manufacture of phosphate fertilizers, as fertilizer for alfalfa (Medicago sativa L.) crops was investigated using pot experiments. The objective of this study was to evaluate the effects of both phosphogypsum and red mud (RM) in two soils representative of the pasture production area in Southern Spain. The morpho-physiological parameters of biomass, plant height, number of stems and number of leaves, as well as the chemical parameters of soil content, were measured. High doses of PG inhibited seed germination in some treatments. In addition, the treatment substrate (2550 g soil + 50 g kg-1 PG + 100 g kg-1 RM) also affected seed germination, possibly due to the large amount of RM. The application of PG and RM to the soil increased the availability of important nutrients for alfalfa, such as phosphorus (P), calcium (Ca2+) and magnesium (Mg2+). The results demonstrate that the treatment with PG significantly improved the uptake of P in alfalfa.

Long-term Exposure to Industrial Chemical Contamination Affects the Magnitude of Predator-induced Immunosuppression in a Free-living Passerine

Industrial chemical contamination is known to have immuno-toxic effects on birds. It may also interfere with natural stressful conditions to further disrupt the immune responses, but these possible interactive effects are still poorly documented in free-living birds. Using the phytohaemagglutinin skin-swelling test, we assessed how the T-cell mediated immune response varied according to the perceived risk of predation in hybrid sparrows, Passer domesticus × Passer hispaniolensis, originating from two sites differentially impacted by industrial chemical contamination, in southern Tunisia. Results showed that T-cell mediated immune response decreased with increasing perceived risk of predation, but the extent of this predator-associated immunosuppression was weaker in birds from the contaminated site compared to those from the control site. The immune response of birds living in the contaminated site was so weak that it could not be further weakened by a predator-related stress. Overall, these results support the idea that chemical contamination interferes with natural environmental stressors, such as predators, thus entailing profound disruption of the immune responses, with possible deleterious repercussions on the ability of birds to cope with diseases.

Formulation of PG-FA-L composite modifier for repairing expansive soil based on the statistical mixed design method

The generation of large amounts of solid waste has led to exploration of solid waste-modified expansive soils; however, the effect of a single solid waste-modified expansive soil is not ideal. This study proposes a composite modification of expansive soils using a PG-FA-L system. Statistical analysis showed that the properties of the cured soil were significantly improved. PG and FA increased soil strength after a certain threshold, and L increased it at all stages. The presence of PG accelerated the volcanic ash reaction. Both PG and FA have a small effect on the swelling of the soil, whereas lime improves it significantly, but has a negative effect after a certain threshold. The 28-day unconfined compressive strength and deformation characteristics were used to derive the relevant regions for roadbed fill requirements and determine the optimum dosage.

Exploring the potential reuse of phosphogypsum: A waste or a resource?

Phosphogypsum (PG), the main industrial by-product of phosphate fertilizer industry, primarily consists of calcium sulfate dihydrate. However, it contains various impurities with variable quantities depending on the origin of the phosphate rock. These impurities can restrict the reuse of phosphogypsum as a secondary primary resource. Consequently, large quantities of produced PG are stored in surface stockpiles that occupy extensive land areas and may pose a significant risk of ecological contamination to the surroundings. Researchers have shown growing interest in addressing the worldwide accumulation of this waste material. To gain a comprehensive understanding of the environmental impact of phosphogypsum, it is crucial to explore its properties (e.g., chemistry, mineralogy, radioactivity), and how it interacts with the surrounding environment, enabling well-informed decisions decision regarding its management and its valorization. In this review, we will i) explore the chemical, radiological and mineralogical characteristics of PG; ii) discuss the environmental concerns related to land discharge and sea disposal; and iii) examine the latest advancements in various valorization techniques developed including agriculture, REE extraction, environmental application, chemical and thermal transformation, and also construction sector. Outlining their limitations and challenges restrict in the global variability of phosphogypsum (PG), technical and economic limitations, and the potential for secondary pollution in select valorization approaches. This requires a thorough assessment and comparison with conventional disposal alternatives.

Effect of alkaline leaching of phosphogypsum on sulfate reduction activity and bacterial community composition using different sources of anaerobic microbial inoculum

Phosphogypsum (PG), a by-product of the phosphate industry, is high in sulfate, (SO42-), which makes it an excellent substrate for sulfate-reducing bacteria (SRB) to produce hydrogen sulfide. This work aimed to optimize SO42- leaching from PG to achieve a high biological reduction of SO42- and generate high sulfide concentrations for subsequent use in the biological recovery of elemental sulfur. Five SRB consortia were isolated and enriched from: IS (Industrial sludges), MS (Marine sediments), WC (Winogradsky column), SNV (petroleum industry sediments) and PG (stored Phosphogypsum). The five consortia showed reduction activity when using PG leachate (with water) as source of SO42- and lactate, acetate, or glucose as the electron donor. The highest reduction rate (81.5 %) was registered using lactate and the IS consortium (81.5 %) followed by MS (79 %) and PG (71 %). To enhance the concentration of leached SO42- from PG for future utilization with the isolated consortia, PG was treated with NaOH solutions (2 % and 5 %). SO42- release of 97 % was achieved with a 5 % concentration and the resulting leachate was further diluted to target a SO42- concentration of 12.4 g·L-1 for utilization with the isolated consortia. Compared to water leachate, a significantly higher reduction rate was registered (2 g·L-1 of SO42) using the IS consortium, demonstrating limited inhibition effect of sulfide- concentration on SRB functionalities. Moreover, metagenomic analysis of the consortia revealed that using PG as a source of SO42- increased the abundance of Deltaproteobacteria, including known SRB like Desulfovibrio, Desulfomicrobium, and Desulfosporosinus, as well as novel SRB genera (Cupidesulfovibrio, Desulfocurvus, Desulfococcus) that showed, for the first time, significant potential as novel sulfate-reducers using PG as a SO42- source.

Sedimentation-Based Separation and Purification of Solid Industrial Waste: A Case Study of Phosphogpusym

The continuous accumulation of solid industry waste, such as phosphogypsum, has emerged as a global environmental hazard and a significant obstacle to achieving a green and sustainable industry. To convert this industry waste to reusable resources, the development and implementation of simple and cost-efficient purification techniques is crucial. A sedimentation-based separation approach was developed to achieve this objective. Through a sedimentation process, a suspension of phosphogypsum particles is transformed into three distinct phases: a supernatant liquid, a concentrated slurry, and a solid precipitate. These phases primarily consist of soluble salts, a mixture of oxides and organic matter, and calcium phosphate dihydrates mixed with calcium phosphate, respectively. Through a sedimentation process, calcium sulfate dihydrate concentration can be significantly enhanced from 87.45 to 91.60% and further improved to 95.72% by repeating the sedimentation process three times. The various components obtained from this process can be effectively reused as mineral resources, soil amendment, and industry gypsum. The sedimentation process is expounded upon using both the classical mechanics model and Stokes' law. To foster a seamless industrial application, we have also designed a continuous settling skittle and a trail setup for industrial treatment of phosphogpysum. This innovative technique holds immense promise for its broader application, especially within but not limited to the phosphoric acid industry.

Influence of partial cement substitution by ground blast furnace slag on the mechanical properties of phosphogypsum cemented backfill

Phosphogypsum (PG) stockpiles occupied a large amount of land resources, and serious environmental pollution problems have attracted the attention of countries around the world. Cemented backfill can reduce the environmental problems caused by tailings stockpiles and is an important development trend in green mine construction. To investigate the effect of binder type on the performance of PG cemented backfill, this paper used ground granulated blast furnace slag (GGBFS) to substitute part of Portland cement (PC) as binder and studied the effect of different ratios of binder on the uniaxial compressive strength (UCS), surface crack extension, acoustic emission (AE) characteristics, and microstructure of PG cemented backfill. The results show that substituting part of PC with GGBFS is beneficial to improve the mechanical properties of PG cemented backfill. When PC was substituted by 50% of GGBFS, the 28d UCS of the backfill was increased from 1.535 to 4.539 MPa. Furthermore, the UCS of the backfill gradually increased as the GGBFS substitution level increased, and more AE signals could be monitored during uniaxial compression. Compared with PC, the sulfate in PG participates in the hydration reaction of GGBFS, more hydrated calcium-aluminum-silicate-hydrate (C-A-S-H) gels and ettringite (AFt) are formed, and the microstructure of the backfill is denser, and the required strength can be obtained with less binder. Thus, substituting part PC with GGBFS as a binder can provide an economical and environmentally friendly alternative for the consumption and reuse of large quantities of PG.

Addition of Phosphogypsum to Fire-Resistant Plaster Panels: A Physic–Mechanical Investigation

Gypsum (GPS) has great potential for structural fire protection and is increasingly used in construction due to its high-water retention and purity. However, many researchers aim to improve its physical and mechanical properties by adding other organic or inorganic materials such as fibers, recycled GPS, and waste residues. This study used a novel method to add non-natural GPS from factory waste (phosphogypsum (PG)) as a secondary material for GPS. This paper proposes to mix these two materials to properly study the effect of PG on the physico-mechanical properties and fire performance of two Tunisian GPSs (GPS1 and GPS2). PG initially replaced GPS at 10, 20, 30, 40, and 50% weight percentage (mixing plan A). The PGs were then washed with distilled water several times. Two more mixing plans were run when the pH of the PG was equal to 2.4 (mixing plan B), and the pH was equal to 5 (mixing plan C). Finally, a comparative study was conducted on the compressive strength, flexural strength, density, water retention, and mass loss levels after 90 days of drying, before/after incineration of samples at 15, 30, 45, and 60 min. The results show that the mixture of GPS1 and 30% PG (mixing plan B) obtained the highest compressive strength (41.31%) and flexural strength (35.03%) compared to the reference sample. The addition of 10% PG to GPS1 (mixing plan A) improved fire resistance (33.33%) and the mass loss (17.10%) of the samples exposed to flame for 60 min compared to GPS2. Therefore, PG can be considered an excellent insulating material, which can increase physico-mechanical properties and fire resistance time of plaster under certain conditions.

PET plastics as a Trojan horse for radionuclides

Mismanaged plastic waste interacts with secondary environmental pollutants, potentially aggravating their impact on ecosystems and human health. Here we characterized the natural and artificial radionuclides in polyethylene terephthalate (PET) bottles collected from the industrial littoral discharge of a phosphate fertilizer plant. The activity concentrations in littered bottles ranged from 0.47 (²⁰⁸Tl) to 12.70 Bq·kg^-1 (²²⁶Ra), with a mean value of 5.30 Bq·kg^-1. All the human health risk assessment indices (annual intake, annual effective dose, and excess lifetime cancer risk) estimated for radionuclides associated with ingestion and inhalation of microplastics were below international safety limits. Our results demonstrated that PET can be loaded with natural and artificial radionuclides, and potentially act as a carrier to transfer radionuclides to humans, posing a new potential health risk. Increased use, mismanagement and fragmentation of plastic waste, and continued interaction of plastic waste with radioelements may lead to enhanced radiation exposure in the future.

Economic losses related to the reduction of Posidonia ecosystem services in the Gulf of Gabes (Southern Mediterranean Sea)

In the early XXth century, the Gulf of Gabes in SE Tunisia used to host the most extended Posidonia oceanica seagrass beds in the Mediterranean basin and was a highly productive hotspot of benthic species. Since the 70's, >500 million t of wet toxic phosphogypsum discharges from a fertilizer industrial complex have led to the gradual loss of ∼90 % of its initial surface. This drastic shrinkage is accompanied by significant value losses originated from the direct and indirect-use services of which the most important ones are small scale fisheries and carbon storage function. Using market valuations of a number of services we estimate economic losses at 105 million € in 2014 (∼915€/ha), i.e., around 115 % of the added value of the gabesian fertilizer factories for the same year. Value losses should increase in the near future in relation with the COP26 agreements which boosted the open carbon credit market. Without actions to reduce negative production externalities caused by the fertilizer industry in the Gulf of Gabes it would not be possible to recover Posidonia ecosystems in this region leading to further economic, ecologic, and cultural losses.

Intra-soil waste recycling provides safety of environment

Amelioration and remediation technology was developed for phosphogypsum utilization in Haplic Chernozem of South-European facies (Rostov Region). The technology comprises phosphogypsum dispersed application into the soil layer of 20-45 cm during intra-soil milling. In the model experiment, the phosphogypsum doses 0 (control), 10, 20, and 40 t ha^-1 were studied. The Cd thermodynamic forms in soil solution were calculated via the developed mathematical chemical-thermodynamic model and program ION-3. The form of ion in soil solution (or water extract) was considered accounting the calcium-carbonate equilibrium (CCE) and association of ion pairs CaCO₃⁰; CaSO₄⁰, MgCO₃⁰, MgSO₄⁰, CaHCO₃⁺, MgHCO₃⁺, NaCO₃^-, NaSO₄^-, CaOH⁺, MgOH⁺. For calculation of the equilibrium of microelements concentration in soil solution ion including heavy metals (HMs), the coefficient of microelement association k_as was proposed. According to calculations, Cd²⁺ ion in soil solution was mostly bounded to associates CdOH⁺, partly to associates CdCO₃⁰ and CdHCO₃⁺. The calculated k_as of Cd was 1.24 units in the control option of experiment and decreased to 0.95 units at phosphogypsum dose 40 t ha^-1. The ratio of "active [Cd²⁺] to total Cd" reduced from 33.5% in control option to 28.0% in the option of phosphogypsum dose 40 t ha^-1. The biogeochemical barrier for penetration of HMs from soil to plant roots was high after application of phosphogypsum. According to calculation by ION-3, the standard soil environmental limitations overestimate the toxicity of Cd in soil solution. New decision for intra-soil milling and simultaneous application of phosphogypsum was developed to provide the environmentally safe waste recycling.

Microbial transformations by sulfur bacteria can recover value from phosphogypsum: A global problem and a possible solution

Rising global population and affluence are increasing demands for food production and the phosphorus (P) fertilizers needed to grow that food. Essential are new approaches for managing the growing amount of phosphogypsum (PG) that is a by-product of phosphoric-acid production from phosphate rock. Today, only ~15% of the worldwide production of PG is recycled, mainly for agriculture and road construction. This review addresses microbial valorization of PG through strategies that apply sulfur-transforming bacteria: sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). The focus is on recovering elemental sulfur (S⁰), which can be used to make the sulfuric acid needed to produce phosphoric acid from rock phosphate. Our review provides in-depth understanding of the microbiological, chemical, and technological bases for microbial reclamation of S⁰ from PG. The review presents the principles and practices for sulfate leaching from PG, reduction of sulfate to sulfide by SRB, and oxidation of sulfide to S⁰ by SOB. The choice of electron donor for SRB, control of oxygen delivery to SOB, and nutrient requirements are emphasized. Although microorganism-based technologies for PG reclamation are far from mature, the efficiency of such SRB- and SOB-based processes has been documented at laboratory and industrial scales. This review should spur biotechnological advances toward recovering value from PG.

Behavioral fever in Bosk's fringe-toed lizards (Acanthodactylus boskianus) living in an industrial area in south-eastern Tunisia

As an indicator of physiological state of lizards, thermoregulatory behavior has been proposed as an assessment tool of environmental contamination, particularly in desert ecosystems where lizards represent a major biological component. Although pesticide contamination has been shown to induce behavioral fever in lizards, the possible pyrogenic effect of heavy metals has received less attention. The objective of this study was to provide data on this issue by using Bosk's fringe-toed lizards (Acanthodactylus boskianus) living in a metal-contaminated industrial area in south-eastern Tunisia as a study model. Combining field observations of behavior with measures of thermoregulatory performance under laboratory conditions, we found that proximity to the industrial zone was associated to a different thermoregulatory behavior of lizards. There was a tendency of lizards living close to the contamination source to display behavioral fever, as they spent more time in the sun, preferred higher body temperatures, and warmed up faster, compared to lizards living far away. This heat-seeking behavior is likely a reaction to improve the functioning of physiological systems involved in the defense against toxic effects of heavy metals, possibly through the increase of metabolic rate, stimulation of enzymes involved in the detoxification process, and enhancement of immune defense systems. Our findings stress the need for further detailed studies into the physiological mechanisms linking metal contamination to behavioral fever. They also underline the usefulness of thermoregulatory behavior as a reliable, non-destructive, and inexpensive, individual-level biomarker in lizard ecotoxicology and biomonitoring of contaminated desert environments.

Bibliometric analysis of phosphogypsum research from 1990 to 2020 based on literatures and patents

The demand together with the urgency of phosphogypsum (PG) treatment will pose significant challenges for many countries. This research aims to explore the research progress of PG, including basic status, cooperation situation, research fields, and development trends, based on the Web of Science database through bibliometric analysis of publications (articles and patents) from 1990 to 2020. The results show that academic research on PG originated early, but the number of patents grew quickly. China is a global leader in terms of the number of publications and plays a significant role in international cooperation. The knowledge of PG has remained concentrated in the fields of natural radioactivity, cement paste backfilling, soil, crystal morphology, and synthetic gas. However, academic hotspots focus on the microstructure of chemical processes and various environmental impacts; patents and hot technologies are based on the production of refractory materials, ceramics, surface materials, cement mortar, and composite materials. The academic frontiers of PG will be centered on exploiting the methods of recovering rare earth elements from PG, the conditions of ion solidification/stabilization in PG, the impact of reaction conditions on product quality, and the reaction mechanism at the micro-level. The frontiers of patents need to focus on the improvement of manufacturing equipment, new wall materials, and chemically modified polymer materials. Envisaging the number of articles and patents to be published in the future, architectural research has a large room for improvement. This paper conducts an in-depth analysis of PG and provides information on the technological development prospects and opportunities, which is helpful for researchers engaged in PG management.

Rare earth elements characterization associated to the phosphate fertilizer plants of Gabes (Tunisia, Central Mediterranean Sea): Geochemical properties and behavior, related economic losses, and potential hazards

This is the first study on the behavior and industrial fluxes of rare earth elements (REE) in the coastal fertilizer plants of Gabes (south-eastern Tunisia), the economic losses related to their wastes, and their environmental and human health hazards. The concentrations of 16 REE were assessed in phosphate rock (PR), phosphogypsum (PG) and phosphogypsum foam (PGF) samples, collected from Gabes plants. REE concentrations ranged from 0.23 (for Sc in PG) to 309.33 mg kg^-1 (for Ce in PGF). Ce was the most abundant in the three matrices, with concentrations ranging between 80.40 (in PG) and 309.33 mg kg^-1 (in PGF). PGF was the most enriched with REE (1075.32 mg kg^-1). The annual flow of REE from the fertilizer factories to the marine environment may reach 1523.67 t. The economic losses related to the discharge of phosphogypsum REE in the Gulf of Gabes (GG) was estimated at ~58 million US$ y^-1. The potential hazards of discharged REE on the local environment and human health were also evaluated and discussed. These findings show the need for the development of a new industry exploiting REE from phosphogypsum wastes (short term) and phosphate ores (long term) which should lead to reduce its high environmental and human health footprint and to potential economic gains.

Dispersion of hazardous nanoparticles on beaches around phosphogypsum factories

Anthropogenic occurring nanoparticles (NPs) have been one of the principal catalytic components of marine pollution throughout its history. The phosphogypsum (PG) factories present environmental risks and evident marine pollution in different parts of the world. Many of these factors continue to operate, however, some have already been abandoned by the private sector. The general objective of this manuscript is to analyze the real nanoparticles (NPs) present on a beach in southern Brazil to illustrate the need to create public policies and projects for environmental recovery. This work focused on real representative sampling of suspended sediments (SSs), and on a modern analytical procedure via advanced electron microscopes (field emission scanning electron microscope-FE-SEM and high resolution transmission electron microscope-HR-TEM coupled with an energy dispersive X-ray microanalysis system-EDS) to analyze NPs containing hazardous elements (HEs). The results presented in this work demonstrate who the size, morphology, among other physical-geochemical characteristics influence in the adsorption of HEs by the NPs and their respective agglomerates. This study is of great importance for carrying out the application of advanced techniques and methods to better understand the formation and transport of NPs on beaches, which allows assisting in the management of waste from plaster factories on a global scale.

Health risk assessment of heavy metals exposure via consumption of crops grown in phosphogypsum-contaminated soils

The management of phosphogypsum (PG) heap, located south of the Sfax city in Tunisia, has been going on for decades. But dumping this solid waste still poses environmental problems. Even though valorized as amendment to agriculture soils, the sanitary impact of this practice is not seriously considered. To assess the risk of the transference of contaminants from PG to agricultural soil-plants food chain, a wild plant species Salicornia arabica grown in PG-contaminated field and tomato (Lycopersicon esculentum) and oat (Avena sativa) grown in laboratory using different rates (10, 20 and 30%) of PG amendment, were tested. The cadmium, lead, chromium, nickel, copper and zinc concentrations in soils and plants were determined by atomic absorption spectrometry and by inductively coupled plasma-mass spectrometry, respectively. Measurements showed that Ni, Cu and Pb levels in the amended soils were below international standards except for Cd and Cr which exceeded Chinese, FAO/WHO and European allowable standard limits. Gathered results showed that the more the PG rate increases, the more the bioconcentration factors of heavy metals increased in plants, particularly in the roots. This is a prospective study assuming direct or indirect exposure scenario of different human cohorts by consuming varied common food stuffs. The Human Exposure to Soil Pollutants evaluation and United State Environment Protection Agency models were adopted for the hazard quotient calculation to assess the acceptability of sanitary risk related to each metal. The direct and indirect health risk assessments varied in the decreasing order: children, adolescents and then adults. Therefore, the PG amendment must not exceed the rate of 10%.

Phosphogypsum Recycling: A Review of Environmental Issues, Current Trends, and Prospects

The problem of recycling and storage of phosphogypsum is topical for many countries around the world, as it is associated with environmental problems of pollution of water bodies, land, and atmosphere. Therefore, this paper analyzes the directions of phosphogypsum recycling and possible alternatives to its use. The main disadvantages of the existing methods of phosphogypsum processing were identified and trends in this waste management were also considered. Through the VOSviewer programme, a visualization of cluster interconnections was carried out in research publications of various fields of phosphogypsum utilization. Five clusters were formed: a red cluster—phosphogypsum recycling in the construction industry; green cluster—radiation pollution problem of phosphogypsum and phosphate fertilizers; yellow cluster—monitoring migration of phosphogypsum components in the ecosystem, with the mobile forms of heavy metals and their inflow into aquifers from phosphogypsum dumps; blue cluster—use of phosphogypsum in agriculture as an ameliorant and a component of fertilizer; and a purple cluster—the impact of phosphogypsum on microorganisms, particularly in bioremediation processes. Under the proposed integrated biochemical approach, the use of various bioprocesses of phosphogypsum recovery from waste dumps and implementation of new biotechnological solutions for processing phosphorus raw materials are presented.

Decreased Cell-Mediated Immune Response in Bosk's Fringe-Toed Lizards (Acanthodactylus boskianus) Inhabiting an Industrialized Area in Southern Tunisia

Lizards increasingly are recognized as suitable contaminant biomonitors in terrestrial ecosystems. Previously, we have shown that Bosk's fringe-toed lizards (Acanthodactylus boskianus) living close to the Gabès-Ghannouche industrial complex for fertilizer and acid production in southern Tunisia were contaminated by heavy metals. However, the impact of this contamination on lizard health parameters has not been investigated. In this study, we used the phytohaemagglutinin (PHA) skin-swelling test to assess whether the proximity to the industrial complex was associated with notable changes in lizard cell-mediated immune response (CMI). Our results showed significantly lower CMI in lizards living close to the industrial complex compared to those occurring farther away in a similar coastal habitat. Overall, our findings are consistent with the idea of immunotoxic effects of metal contamination. They also stress the usefulness of the PHA approach as an efficient tool for the evaluation of contaminant-related immunosuppression in lizards.

Economic impact of human-induced shrinkage of Posidonia oceanica meadows on coastal fisheries in the Gabes Gulf (Tunisia, Southern Mediterranean Sea)

In early XXth century, the Gulf of Gabes (SE Tunisia) used to host the most extended Posidonia oceanica seagrass beds in the Mediterranean Sea, and a highly productive hotspot of benthic/demersal biodiversity. Sponge harvesting and seabed trawling provoked a first step of seagrass degradation. Subsequently, phosphogypsum releases from Gabes Industrial Complex, since mid-1970s, accelerated the decline of the remaining patches. A sharp reduction of coastal fisheries landings took place with the establishment of the last industrial plant units in 1985. The decrease in coastal commercial species landings was found to be directly correlated with P. oceanica decline. The trophic web system switched from a 'benthic-dominated' to a 'pelagic-dominated' system. The economic loss related to coastal fisheries was estimated at ~60 million € in 2014 and the 1990-2014 cumulated loss exceeded 750 million €. This first economic valuation of the only direct-use consumptive value of the coastal fishing service provided by P. oceanica in Gabes Gulf is a first step towards the assessment of the environmental cost of the negative externalities caused by the local phosphate industry. It may be used as a preliminary decision-making aid to consider alternative industrial solutions.

MerP/MerT-mediated mechanism: A different approach to mercury resistance and bioaccumulation by marine bacteria

Currently, mechanism underlying mercury resistance and bioaccumulation of marine bacteria remains little understood. A marine bacterium Pseudomonas pseudoalcaligenes S1 is resistant to 120 mg/L Hg²⁺ with bioaccumulation capacity of 133.33 mg/g. Accordingly, Hg²⁺ resistance and bioaccumulation mechanism of S1 was investigated at molecular and cellular level. Annotation of S1 transcriptome reveals 772 differentially expressed genes, including Hg²⁺-relevant genes merT, merP and merA. Both merT and merP gene have three complete copies in S1 genome, while merA gene has only one. In order to evaluate the function of these Hg²⁺-relevant genes, three recombinant strains were constructed to express MerA (named as A), MerT/MerP (TP) and MerT/MerP/MerA (TPA), respectively. The results show that Hg²⁺ resistance of strain TP, TPA, and A are improved with minimum inhibition concentration (MIC) being 60 mg/L, 40 mg/L, and 20 mg/L, respectively compared to 2 mg/L of host strain. Strain TP and TPA exhibit enhanced Hg²⁺ bioaccumulation capacity, while strain A does not differ from the control. Their equilibrium Hg²⁺ bioaccumulation capacities are 110.48 mg/g, 94.49 mg/g, 83.76 mg/g and 82.29 mg/g, respectively. Summarily, different from most microorganisms that exhibit Hg²⁺ resistance by MerA-mediated mechanism, marine bacterium S1 achieves Hg²⁺ resistance and bioaccumulation capability via MerT/MerP-mediated strategy.

Molecular speciation of phosphorus in phosphogypsum waste by solid-state nuclear magnetic resonance spectroscopy

Phosphogypsum (PG), a waste by-product of the phosphate fertilizer industry as well as a point-source P contaminant, has caused serious environmental problems particularly in estuarine and coastal regions. However, in-depth understanding of P speciation in PG, which is critical for its restoration and management, remains largely unknown. Using solid-state ³¹P NMR spectroscopy, density functional theory calculations of the NMR parameters and NanoSIMS, we for the first time reported that P in PG ubiquitously exists as phosphate incorporated into gypsum and minor fluorapatite. The occasional presences of mineral phosphate phases mainly associated with Ca and Al were also detected. The molecular environment of the incorporated phosphate is HPO₄^2- substituting for SO₄^2- in the gypsum lattice with the H atom away from the H₂O molecules and almost parallel to the a-c plane. A high spatial heterogeneity was observed for the distribution of this phosphate species in PG at the submicron scale. Upon heating, at least 64% of the incorporated phosphate could be converted to the easy-to-recover fluorapatite or amorphous calcium phosphate by thermal treatments at above 750 °C for 2-4 h. This information of P speciation transformation may pave a solid basement for the sustainable recovery of P from PG.

Natural radioactivity and radiation hazard assessment of industrial wastes from the coastal phosphate treatment plants of Gabes (Tunisia, Southern Mediterranean Sea)

This work is a first contribution to the knowledge of natural radionuclides (²²⁶Ra, ²³⁸U, ⁴⁰K, and ²³²Th) activities in phosphate rock (NORM), phosphogypsum, and phosphogypsum foam (TENORM) from the coastal fertilizer plants of Gabes (Southeastern Tunisia) and the assessment of their radiation hazards on human health and the surrounding environment. In the three studied materials, activities were found to be in the range of 35.4 (⁴⁰K)-375.1 (²²⁶Ra), 10.0 (⁴⁰K)-220.2 (²²⁶Ra), and 79.2 (²³²Th)-1168.6 Bq kg^-1 (²²⁶Ra), respectively. Considering the studied radionuclides and materials, the corresponding decreasing activity orders were found to be ²²⁶Ra > ²³⁸U > ⁴⁰K > ²³²Th and PGF > PR > PG, respectively. All human health hazard indices exceeded the worldwide recommended safety limits, which show that the workers in Gabes phosphate fertilizer plants as well as the neighboring human community may potentially be exposed to significant radiation, which may cause several diseases and malformations. It is therefore recommended to avoid and/or reduce the potential fertilizer industry radioactive impact in the area.

An innovative method for synergistic stabilization/solidification of Mn2+, NH4+-N, PO43- and F- in electrolytic manganese residue and phosphogypsum

Electrolytic manganese residue (EMR) contains large quantities of manganese (Mn²⁺) and ammonia nitrogen (NH₄⁺-N). Phosphogypsum (PG) contains plenty of phosphate (PO₄^3-), fluorine (F^-) and some heavy metals. Separate storage of EMR and PG could seriously damage the ecological environment. In this study, synergistic stabilization/solidification (S/S) of EMR and PG was studied. The effects of EMR:PG mass ratio, S/S pH, solid-liquid ratio and temperature on the concentrations of NH₄⁺-N, PO₄^3-, Mn²⁺ and F^- in the leaching solution, and the characteristics of EMR and PG were studied. Meanwhile, the synergistic S/S mechanisms of EMR and PG, and leaching test were investigated. The results showed that the concentrations of F^-, PO₄^3-, NH₄⁺-N and Mn²⁺ in the leaching solution were 4.5 mg/L, 13.6 mg/L, 55.5 mg/L and 0.8 mg/L, respectively, when the mass ratio of EMR to PG was 1:2 and the pH was 9.0 adjusted by MgO after 20 days S/S. Manganese was mainly solidified as Mn₃(PO₄)₂·7H₂O and Mn(OH)₂, and ammonia nitrogen was mainly stabilized as struvite; fluorine was mainly stabilized as (Mn, Ca, Mg)F₂, and phosphate was mainly solidified as (Mn, Ca, Mg)₃(PO₄)₂ and (Mn, Ca, Mg)HPO₄. The leaching test results showed that PO₄^3- and NH₄⁺-N were reduced to 13.6 mg/L and 55.5 mg/L, respectively, and the concentrations of all the measured heavy metals and F^- were within the permitted level for the GB8978-1996 after 20 days S/S.

Predicting spatial distribution of heavy metals in an abandoned phosphogypsum pond combining geochemistry, electrical resistivity tomography and statistical methods

One of the wastes generated in fertiliser production from phosphoric rock is phosphogypsum, whose mismanagement lead to environmental and health risks. Therefore, a detailed evaluation of the chemical composition of phosphogypsum is necessary to determine effective means of its management. Due to the high amount of generated waste, the cost and time consumed for this characterisation by chemical analysis is limiting. Hence, efficient tools should be developed to predict the chemical composition of this waste. Thus, this study aims to: 1) determine the physic-chemical characterisation of phosphogypsum pond using geochemical and geophysical techniques and 2) predict the heavy metals spatial distribution through statistical models. Results show that the most concentrate metal is chromium with a maximum of ≈900 mg.kg^-1 and cadmium is the least concentrated (maximum ≈23 mg.kg^-1). The Electrical Resistivity Tomography revealed the superposition of two layers. The top one (waste) presents low resistivity (≈17Ω.m) while the bottom layer shows higher resistivity (>124Ω.m). Metal concentrations and resistivities were combined by applying non-linear regression models. Cr showed the strongest correlation (R² = 0.68), yielding an accurate model that was used for revealing the spatial distribution of the highest Cr concentrations in the pond, with the consequent reduction of expensive traditional methods.

Structure of the benthic macrofauna of an anthropogenic influenced area: Skhira Bay (Gulf of Gabès, central Mediterranean Sea)

Skhira Bay located in the Gulf of Gabès, on the southeastern coast of Tunisia, is an important area in terms of its dense vegetation coverage, wide continental shelf, and fisheries resources. However, this area with a typically micro-tidal range is subject to intensive anthropogenic pressures: soft bottom trawling, chemical pollution from phosphoric acid production, and shipping activity. The present study is the first investigation of the structure of the benthic macrofauna on this part of the Tunisian coast. In April 2010, 28 stations were sampled along four transects from the phosphogypsum outfall on an inshore-offshore gradient. A total of 239 macrobenthos taxa, belonging to nine zoological groups and 140 families, were identified with a dominance of polychaetes (33.5%), crustaceans (29.4%), and mollusks (19.6%). Results show that the stations facing the phosphogypsum discharges are the most disturbed and characterized by a poorly diversified macrofauna. The macrofauna is dominated by carnivores, suspension feeders, and selective deposit feeders, and seems to be linked more to the availability of trophic resources than to disturbance. Four benthic assemblages are identified using Cluster and MDS analyses linked to edaphic factors, such as sediment structure, organic matter content, inshore/offshore gradient, and the proximity of the phosphogypsum outfall. The biotic indices (AMBI and BO2A) calculated from macrofauna data show that the ecological status of Skhira Bay varies overall from moderate to good. This study suggests initiating a long-term monitoring program to improve our understanding of the temporal changes of this ecosystem, to recommend the necessary conservation measures in this area of high-value natural heritage.