Phosphogypsum foam: a vector of industrial pollution affecting Mediterranean biodiversity and the health of coastal populations in Gabès (SE Tunisia)

This study focuses on phosphogypsum foam from marine discharges from phosphate fertilizer plants in Gabes (SE Tunisia). Its formation process includes three main steps: (i) formation by dissolution of phosphogypsum (a toxic radiochemical by-product from phosphoric acid production), (ii) stabilization by organic surfactants (surfactants) and gypsum crystals, and (iii) geochemical and/or mechanical destabilization. This research is an important part of the response to the pollution problems caused by the phosphate fertilizer industry worldwide, especially in developing countries.

Phosphogypsum (CaSO4·2H2O), a radiochemical by-product of phosphoric acid (H3PO4) production, has been dumped untreated into the Gabes Sea since 1972, in the form of gypsum slurry. Tunisian phosphate processing plants, known as Groupe Chimique Tunisien (GCT), after a sulfuric attack of phosphate ore (fluorapatite) from the Gafsa mining basin (SW Tunisia), produce phosphoric acid and various phosphate fertilizers, such as mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP), simple super phosphate (SSP) and triple super phosphate (TSP), as well as di-calcium phosphate (DCP). For each ton of phosphoric acid produced, approximately five tons of phosphogypsum are generated. Since the 1970s, the quantities discharged into the sea of ​​Gabès have largely exceeded 500 million tonnes of wet phosphogypsum. This industrial pollution has devastating consequences on marine and terrestrial fauna and flora, and also the health of local coastal populations.

During its discharge into the sea, the gypsum slurry (or gypsum water) forms a spectacular dark brown to blackish foam, which contains very high levels of toxic trace elements (U (56 mg/kg), Cd (50 mg/kg), As (30 mg/kg)…), radionuclides (226Ra (1169 bq/kg), 238U (626 bq/kg), 232Th (79 bq/kg)…), and rare earths (Ce (309 mg/kg), Nd (196 mg/kg), Y (195 mg/kg)…), has not been studied until now. This study was conducted by the Laboratoire Géosciences Environnement Toulouse, in collaboration with other laboratories and international research centers (IRAP, France), the Raimond Castaing Micro-characterization Center (France), and the National Institute of Oceanography and Applied Geophysics (Italy).

This study showed that the foam formation process involves three main steps: (i) formation (by dissolution of phosphogypsum), (ii) stabilization (facilitated by organic surfactants (surfactants) and gypsum crystals), and (iii) geochemical (involving dissolution of gypsum from the foam skeleton) and/or mechanical (influenced by wind and wave action) destabilization. Due to its amphiphilic nature (possessing both a hydrophilic (polar) and a second lipophilic (apolar) phase), and the presence of certain organic groups (e.g. -OH, R-S-R, and R-N-R), foam retains high levels of toxic contaminants, inherited from phosphogypsum, such as trace elements, radionuclides, and rare earths, making it an important vector of marine pollution. This potential load of toxic contaminants threatens the marine and terrestrial environment (fauna and flora), as well as the health of coastal populations in Gabès. Indeed, this foam plays the role of the main agent of accumulation, transport and dispersion of radiochemical pollutants (inherited from phosphogypsum and other untreated industrial waste discharged into the sea) in the Gulf of Gabès.

The consequences of this industrial pollution are very serious, especially for local populations. Indeed, residents of the Gabes region, particularly those of the maritime oasis of Chatt Sidi Abd Essalam (East of Gabes), who are chronically exposed to toxic radiochemical contaminants from phosphogypsum foam via several routes (mainly through direct exposure to radioactivity from the foam, contact with contaminated seawater, consumption of contaminated fish, and inhalation of volatile particles from dried foam on the beach).This industrial pollution (via phosphogypsum foam and other untreated industrial discharges (solid, liquid and gaseous)) is associated with various health problems that are widespread in Gabès, such as cancers (lung, nose, breast, liver, kidney, stomach, blood (leukemia), brain or spinal cord (gliomas) …), congenital malformations (septal malformations, limb anomalies (syndactyly and agenesis), facial malformations (facial dysmorphia), cranial malformations (brachycephaly), heart malformations (single ventricle) …), membrane paralysis (paraplegia and quadriplegia), chronic diseases (respiratory diseases (asthma, allergies, chronic obstructive pulmonary disease …), cardiovascular diseases (stroke, myocardial infarction, high blood pressure, cardiac arrest …), and other health problems (bone fluorosis, osteopor … dental, infertility and sexual impotence in both sexes, repeated abortion, premature birth, miscarriage, etc.).

These diseases lead to a remarkable premature mortality and an increase in the number of cardiovascular and cancer deaths, particularly among workers and residents living around the phosphate processing plants in Gabès (Chatt Sidi Abd Essalam, Ghannouche and Bouchemma). The environmental impacts are also significant, with many cases of marine animals (sea turtles (Caretta caretta), seabirds (Sterna hirundo, Chroicocephalus ridibundus, Phalacrocorax carbo…), marine mammals (Tursiops truncatus), fish (Belone belone, Liza saliens, Dicentrarchus labrax…)) malformed or dead found on the beach of Chatt Sidi Abd Essalam (receptacle for all the different untreated solid residues (sulfur dross, used catalysts, raw phosphate…) and liquid (gypsum water, fluoridated water, cooling water…) from the chemical plants in Gabès, called by the locals as ‘the cemetery of the Mediterranean’.

This research is an essential response to the pollution problems generated by the phosphate fertilizer industry not only in Tunisia but also throughout the world. Indeed, phosphogypsum does not only represent a threat to developing countries (Tunisia, Morocco, Algeria, Lebanon, Syria, etc.), but also constitutes a global issue, affecting developed countries such as Spain, Canada, the United States, Finland, Greece and China. Thus, the relocation of this highly polluting industry to third world countries, often without strict regulations, or to countries with more lax legislation, will not solve the environmental and health challenges posed by this industry, in a context where pollution has become a global concern.

Contacts GET: Michel Grégoire and Sylvie Castet