The Mediterranean basin is notoriously contaminated by products and residues resulting from human activity. These contaminants concentrate in continental waters (rivers, groundwater, etc.), which carry them to the sea. Until now, the study of water contamination has often been approached in a fragmented way, either by study medium (surface or underground water, ocean, etc.) or by speciality (biologists, ecologists, epidemiologists, etc.). Similarly, environmental chemists often focus on a small number of contaminants, linked to a research theme based on a specific family of analysis or sampling methods. Although essential, these approaches do not allow us to understand the strong interactions that exist between the various contaminants in the natural environment ('cocktail effect' on toxicity, catalytic effects of metals, bactericidal effects of antibiotics and pesticidal effects of fungicides).
The Bizerte lagoon, in northern Tunisia, is known for being the site of numerous urban, agricultural, industrial and port activities, which generate a multi-contamination impact on its biodiversity and aquaculture productivity. One of these tributaries, the Oued Gueniche, presents a particularly appropriate context in which to test an interdisciplinary approach that considers most of the contaminants together. Under the MISTRALS programme, a Franco-Tunisian team has been conducting an original study over the past two years, combining biologists, hydrologists, hydrogeologists and agronomists with specialists in contamination by (organo)metals and organic substances (pesticides, emerging substances). As part of this collective effort, each person is simultaneously determining 'their' measurements so that information can be cross-referenced at a later date.
The initial results obtained are promising, as they support the value of an exhaustive and collaborative approach. They show the presence of 41 quantified contaminants in the wadi water (20 active pesticide substances and metabolites, 14 emerging molecules, mainly pharmaceuticals, 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. During the rainy season, the wadi draining the water table and treated soils could explain some of the pesticide levels observed.
This is a huge challenge for this Franco-Tunisian team, who will have to carry out a large number of varied measurements before pooling their expertise and comparing their interpretations to achieve a better understanding of the processes involved in cases of multi-contamination of the natural environment. In addition, the identification of contaminant interactions with the organisms present in these environments (larvae, molluscs, etc.) should be a particularly important outcome of this project.
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