La contamination du Léman par les micropolluants : revue de 40 ans d'études

Lake Geneva pollution by micropollutants – a review of 40 years of study. – Lake Geneva drains a watershed of about 8000 km2, subject to anthropogenic pressures due to a large population, agriculture, and industries. Contaminants released by these activities may eventually end up in the lake water, sediments and biota. For more than 40 years, the International Commission for Lake Geneva Protection (Commission Internationale pour la Protection des Eaux du Léman), and research institutes located around the lake, look after these contaminants by following the evolution of analytical technics. This review particularly focuses on the evolution of the lake contamination by mercury, PCBs, pesticides, drugs and some emerging pollutants. Mercury and PCBs were the first contaminants detected in sediments in the 1970s. These contaminants were particularly targeted because of their propensity to bioaccumulate in organisms and biomagnify in the food chain, and because of their high ecotoxicity. If the contamination of fish by mercury seems controlled with values ~10 times lower than the legal limits, PCBs still pose problems for fatty fish such as Arctic char (Salvinus alpinus). Improved techniques for analyz- ing organic products revealed the presence in the waters of more than one hundred pesticides and thirty pharmaceuticals. In addition, contamination of Foramsulfuron in 2005, from industry, has almost reached the legal limit for drinking water. This review shows that the contamination of the lake over the last 40 years has evolved with the growing presence of many contaminants, either by the release of new substances or by improving analytical techniques. Monitoring of water quality is essential to act early enough to reduce inputs in the lake. And special vigilance must be maintained for both ‘old’ pollutants (Hg, PCBs) and emerging contaminants such as pharmaceuticals, microplastics, and products of industrial synthesis.