Nouvelle technique pour tester in situ l’impact de pesticides sur la faune aquatique non cible

Résumé Fr En

Après avoir réalisé plusieurs séries d’expérimentations, en laboratoire et dans le milieu naturel, afin de tester l’impact de nouveaux insecticides sur la faune aquatique non cible, nous avons pu juger les avantages et les inconvénients liés à ces 2 techniques. Afin d’améliorer la représentativité des résultats obtenus, nous proposons une technique nouvelle d’expérimentation qui tout en gardant les avantages des méthodes classiques, en supprime les inconvénients. Cette méthode utilise un modèle réduit de cours d’eau, installé in situ et dont l’utilisation permet la mise en évidence de la sensibilité des différents organismes testés vis à vis du pesticide expérimenté.Un premier essai de l’appareil a donné des résultats qui confirment ceux obtenus par d’autres méthodes.

Lethal effects of new pesticides on non-target organisms are often estimated on the basis of laboratory bioassays. The relevance of such experimental data to natural conditions is questionable. In other respects, field trials mode on a large scale, can have unexpected and noxious effects on the aquatic environment.Our purpose was to carry out a new in situ method having the same accuracy as laboratory tests. The environmental conditions of the treated area are simulated.The method is based on the utilization of one apparatus which has been specially designed and which represents a reduced model of a river bed. It is made of sheet-iron, and ils lower part is closed by removable drift-net.The pesticide formulation to be tested is kept in a storage tank, set up above the upper part of the apparatus and can flow regularly into the System. This device is anchored into shallow and running water beds. Different types of substrates (sand, gravels, stones, etc.), containing fauna, are transferred into the U-shaped part of the apparatus, and this one is kept open at both ends during 12 h for recovering. After this preparation phase, the lower part is closed with a drift-net and the pesticide solution is allowed to flow down, during a given time.Samples are taken successively, after 30 minutes, I, 2, 4, 8 and 24 h by removing the drift net collector. Finally, the substrates are taken off and the remaining fauna, not killed by the pesticide, is sorted by washing and sieving the sediment, after fixation into formalin. The total amount of experimented fauna is equal to the sum of killed fauna present in collectors plus living fauna which remains at the end of the bio-assay.The degree of susceptibility of experimented species can be derived from quantitative analysis of the different samples and curves depicting specific drift-rates versus time can be drawn. By that method sufficient numbers of organisms are tested and therefore, specific reactions related to different pesticides can be assessed statistically.