Résumés
Résumé
L'eau interstitielle ou l'eau de lessivage d'un sédiment est mise en contact avec des lots de 50 femelles ovigères du copépode Tigriopus brevicornis. Notons que ce microcrustacé marin est sensible à la pollution mais résistant aux caractéristiques physico-chimiques des types d'eaux testés (salinité et température notamment). On évalue ensuite les effets de ces eaux sur la production larvaire en 10 jours et sur l'ingestion en 4 jours par les copépodes d'une suspension de Phaeodactylum tricornutum. Nous observons ici, pour des lots de sédiments provenant de la région de Marseille, des réductions de la production de larves variant de 61 % (Les Embiez) à 90 % (Vaine). Le test "consommation d'algues", bien moins sensible aboutit pour les mêmes stations à des réductions de 19 % à 35 %. Le test "production larvaire" du fait de sa plus grande sensibilité doit être préféré au test "consommation d'algues".
Mots-clés:
- Toxicologie,
- pollution du sédiment,
- copépode,
- production larvaire,
- consommation d'algues
Abstract
Most pollutants discharged into the sea are found in sediments, generally after temporary fixation in planktonic organisms. The slightest discharge leaves a trace in the soft bottoms. Thus, it may be said that these behave as good "data storage indicators" testifying to the degree of pollution present. Sediments therefore represent a privileged field in research on the state of pollution in the aquatic ecosystem. How can the degree of pollution in this field be evaluated?
A chemical analysis of pollutants in sediments is a good means of investigation to detect of degradation in the quality of waters. Most pollutants however are difficult to detect and dose. Moreover, in many cases dosage is tedious and costly. It is from this point of view that biological assays were considered essential.
Interstitial water or water used to wash a sediment was placed in contact with batches of 50 ovigerous females of the copepod Tigriopus brevicornis. This marine microcrustacean is known to be sensitive to pollution, though resisting the physical and chemical effects of the waters tested (salinity and temperature, in particular). An evaluation was the made on the effects of these waters; first on larval production during a period of ten days, and then on ingestion by copepeds of a suspension of Pheodactylum tricornutum for four days.
The results obtained here with batches of sediment from the Marseilles region show that the larval production test is the most sensitive one. Indeed, the inhibition percentages found by the larval production test range from 35 to 100 % (figure 1), whereas they vary from 5 to 55 % with the algae consumption test (figure 2). With the larval production test, it is possible to classify sediments according to their ecological quality.
From this test, moreover, the presence of harmful substances in the sediments can be rapidly detected. Being reproductible and not expensive, it supplements the far too restrictive traditional chemical analyses. When applied to estuarine sedimentary zones, combined with other tests, it should help establish a quality coefficient for sediments based on experimentation.
Keywords:
- Toxicology,
- pollution of sediment,
- copepods,
- larval production,
- consumption of algae