Gulf of Gabès (Groupe Chimique Tunisien complex)

The complex of the state-owned Groupe Chimique Tunisien was inaugurated in 1972 on the coast between Gabès and Ghannouch, next to a coastal oasis of about 300,000 date palms. It processes phosphate from the Gafsa basin into fertilisers; the last units came on stream in 1985. The by-product, phosphogypsum, is discharged untreated into the open sea.

Phosphogypsum carries the trace elements of the phosphate rock. In the surface sediments off the complex, cadmium and zinc derive mainly from the phosphogypsum, with the highest ecological risk in the zone between the two harbours (El Zrelli et al. 2015). The annual flow of fluorine to the sea has been estimated at about 87,250 tonnes (El Zrelli et al. 2018). As it dissolves, phosphogypsum forms floating foams that concentrate metals and radionuclides and carry them far from the outfall: radium-226 activities of up to 1,168.6 Bq/kg have been measured in them (El Zrelli et al. 2019).

In the early twentieth century the gulf held the most extensive Posidonia oceanica meadows in the Mediterranean. Sponge harvesting and trawling had already damaged them; the discharges accelerated their decline, to a loss of about 90% of the original surface. The economic loss to coastal fisheries was estimated at about 60 million euros in 2014, and at more than 750 million cumulatively between 1990 and 2014.