Meeting the challenge of multi-contamination of Mediterranean waters

The Mediterranean basin is notoriously contaminated by products and residues from human activity. These contaminants are concentrated in continental waters (rivers, groundwater,...) which transport them to the sea. Until today, the study of water contamination was frequently approached in a fragmented way, either by study medium (surface or sub-surface water, ocean,...), or by specialties (biologists, ecologists, epidemiologists,...). Similarly, environmental chemists often focus on a small number of contaminants, linked to a research theme supported by a specific family of analytical or sampling methods. Although essential, these approaches do not allow us to understand the strong interactions that exist between different contaminants in the natural environment ("cocktail effect" on toxicity, catalytic effects of metals, bactericidal effects of antibiotics and finally pesticidal effect of fungicides).

The lagoon of Bizerte, in the north of Tunisia, is known to be the place of concentration of multiple urban, agricultural, industrial and port activities that generate a multi-contamination impacting its biodiversity and aquaculture productivity. One of these tributaries, the Oued Gueniche, presents a particularly appropriate context to test an interdisciplinary approach that considers most of the contaminants together. By joining forces under the MISTRALS program, a Franco-Tunisian team has been conducting an original study for the past two years in which biologists, hydrologists, hydrogeologists and agronomists are associated with specialists in contamination by (organo)-metals and organic substances (pesticides, emerging). In this collective effort, each one determines in parallel 'his' measurements so that the information can be crossed later.

The first results obtained are promising because they support the interest of an exhaustive and collaborative approach. Indeed, they show the presence in the wadi water of 41 quantified contaminants (20 active pesticide substances and metabolites, 14 emerging molecules, mainly pharmaceutical, and 7 metals). Twenty-eight molecules were measured at least once at a value greater than 0.1μg/L. Locally, groundwater is little affected by this contamination, which seems to affect only part of the water table during periods of heavy irrigation. In the rainy season, the wadi draining the water table and the treated soils could explain some of the observed pesticide levels.

The challenge is immense for this Franco-Tunisian team, which will have to carry out a large number of varied measurements before combining their expertise and comparing their interpretations to achieve a better understanding of the processes involved in cases of multi-contamination of the natural environment. Moreover, the identification of contaminant interactions with organisms present in these environments (larvae, mollusks,...) should be a particularly important result of this project.

Authors and authors

Olivier Grunberger , Chrystelle Bancon-Montigny, Mustafa Bejaoui, Ines Sahraoui3 Radhouane Hamdi1 Safouan Ammar4, Hanene Chaabane, Manon Lagacherie, Jean-Denis Taupin, Walid Chmingui, Olfa Mahjoub, Asma Sakka, Olivier Pringault