Application de microbiotests en kits (Toxkits) dans la caractérisation de la toxicité des eaux usées de la ville de Fès (Maroc)

Application of kits microbiotests (Toxkits) in toxicity characterization of wastewater's of the city of fes (Morocco)

¹ Laboratoire de Biotechnologie. Faculté des Sciences et Techniques, Fès- Saiss. Route d'Immouzer, BP 2202. Fès (Maroc)
² Laboratoire d'Hydrobiologie et Ecologie Générale. Faculté des Sciences Dhar el Mehraz Fès (Maroc)

Résumé

En Ecotoxicologie, l'évaluation de l'impact des eaux usées et des polluants divers de l'environnement implique l'utilisation de matériel biologique spécifique et sensible tel que le test Algue ou le test Daphnie. Cette technique se base essentiellement sur la maintien des organismes tests en vie, dans de bonnes conditions de culture et en nombre suffisant. Cependant, de telles cultures nécessitent un équipement important et un entretien permanent. De ce fait, les biotests ne peuvent être pratiqués que dans des laboratoires spécialisés et restreints en raison du coût élevé de ces opérations. Actuellement, il devient possible d'effectuer des tests de toxicité en routine, à coût intéressant et nécessitant un équipement simple et miniaturisé (Toxkit) en utilisant simplement des « oeufs dormants » ou kystes d'organismes aquatiques spécifiques comme matériel d'expériences. Ces kystes peuvent se conserver longtemps sans perdre leur viabilité et sont aptes à éclore en 24 heures libérant des individus qui sont utilisés directement dans les tests de toxicité.

Dans ce travail, une étude de la toxicité aiguë des eaux de surface de 3 bassins hydrographiques de la ville de Fès est réalisée. Ces bassins reçoivent des rejets de nature diverse, effluents domestiques, industriels ou mixtes. Les tests de toxicité sont effectués avec des kystes appartenant respectivement à Daphnia magna (Daphtoxkit), à un Rotifère Brachionus calyciflorus (Rotoxkit) et à un Crustacé, Thamnocephalus platyurus (Thamnotoxkit). Les résultats exprimés en unités de toxicité (UT) montrent que les eaux de surface des bassins étudiés présentent une toxicité qui varie de 0 à 20 UT. La majorité des stations étudiées sont classées toxiques pour les organismes aquatiques, ce qui représente un danger potentiel pour l'environnement et l'Homme, et amène à prendre des mesures urgentes de traitement et de valorisation de ces eaux.

Abstract

The assessment of the hazard to the environment resulting of toxic pollutants presents in wastewaters discharges is in many countries, still performed exclusively by chemical analyses. However, During recent years, it has became generally accepted that chemical data by themselves do not allow to evaluate the global toxic effect of pollutant. In fact, such approach suffers from a number of shortcoming:

- The large number and the diversity of toxic substances potentially presents in the wastes.

- The limitation in practice of the number of chemical analyses performed

- The difficulty in extrapolating the real hazard of wastewaters, from the chemical data (different compounds present in different concentration).

- The inability to predict the interactive effect of the toxicants.

As a result, for a realistic estimation of the hazard of wastes discharges, increasing attention is to date focussed on the incorporation of biologicals tests. Bioassays are generally perfomed with aquatic organisms such as fish, crustacean or microalgae. Unfortunately, biologicals testing also suffers from a number of disadvantages, of wich the major one is the need for continuous culturing and maintenance of live stocks of tests organisms in sufficient numbers and in a healthy state. Consequently, such assays are only carried in specialized laboratories and in limited number because of the high costs. To date, however, it has become possible to do acute testing in routine, at low cost and without any need for sophisticated equipment simply by using «dormant eggs» or cysts of specific species of aquatic biota as «starting» biological materiel. Such cryptobiotic eggs can be stored for long periods without losing their viability and hatched at will in 24 hours of time. This new concept eliminates the (very expensive) continuous culturing or maintenance of tests organisms. Standardized tests procedures for acute screening tests have been developed with freshwater and estuarine/marine rotifers and crustaceans. These tests have recently been miniaturized in toxkits to optimize their cost-effectiveness.

This study shows acute toxicity of surface wastewaters of 3 rivers of the city of Fès (Morocco). These rivers are receptors of several domestic and industrial effluents. 44 samples were collected from differents points within the rivers, for several days and assessed with a battery of new microbiotests (cyst based toxkits) comprising the Daphnia magna bioassay (Daphtoxkit), The Rotoxkit with the freshwater rotifer Brachionus calyciflorus and the Thamnotoxkit test with the freshwater fairy shrimps Thamnocephalus platyurus. Chemical analyses were performed for conventional water quality parameters such chemical oxygen demand (COD), biological oxygen demand (BOD5), NH3; NH4+, 02, and pH. Toxicity of the samples expressed in toxics units (UT) was found to vary between 0 and 20. The majority of examined rivers samples have showed to be classified as toxic for aquatic biota, which requiered an emergency control and treatment.

Relationships between the chemical composition and the toxicity of the effluents could be established in some cases, but not in others, which confirms the difficulties of extrapolating toxic hazards of complex wastes from (mostly restricted) chemical analyses.

The present research demonstrate the potential and sensitivity of cost- effective microbiotests (cyst based toxkits) as attractive alternatives for routine monitoring of effluents and wastes.