La bioconcentration du Zn, Cu et Cd a été étudiée chez Melanopsis praemorsa L. (Gastéropode prosobranche) provenant de deux sites d'une khettara située dans le champ d'épandage des eaux usées de la ville de Marrakech. Les khettaras représentent un système d'irrigation traditionnel que l'on trouve dans certaines zones arides et semi-arides de la région ouest-paléarctique. L'eau est mise à jour par drainage de la nappe phréatique. Le degré de contamination de ce gastéropode s'avère très élevé et les teneurs métalliques augmentent de l'hiver à l'été. Les causes de la variabilité des concentrations métalliques chez les gastéropodes des deux stations ont été recherchées par des expériences de transplantation, et par des dosages de métaux au niveau du sédiment, de la spirogyre et du périphyton installé sur des substrats artificiels. Les résultats obtenus montrent que les différences entre les concentrations métalliques accumulées par les Melanopsis dans les deux stations pourraient être attribuées à la spéciation du métal dans l'eau. D'autres facteurs peuvent être mis en cause et méritent d'être précisés.Molluscs are well known for their capacity to bioaccumulate heavy metals from water or sediments. This study involves an evaluation of the contamination level of the undergroud and surface waters from a specific irrigation system known as a « khetarra », located near the town of Marrakech (Morocco). Khettaras represent a traditional systern by means ofwhich the ground water is drained to the surface and then can be used as drinking water or for irrigation in some arid and semi-arid areas. The bioindicator chosen was the gasteropod Melanopsispraemorca L. Two stations (Kl and K2) were investigated in a khettara located in spreading Marrakech waste water. The contamination of soils and water by heavy metals, eipecially Zn, Cu and Cd was first described by EL MEZD1 (1985) and SEDKI(1990).The studied khettara (1500 m. in length) is contaminated in two different ways: first by infiltration of waste water from the Seguia system and secondly directly by over-flow and escape of a main common sewer which crosses over the khetarra between the Kl andK2 stations.At each station, sediment peripbyton, Spirogyra and M. praemorsa were sampled in different seasons. Each sample was prepared for analysis (S.A.A. varian 475.AA) according to the method described by COSSON (1987). Flame atomization was chosen for Zn and Cu, the grafite furnace for Cd.The main results concern the level of contamination, with a comparison between Kl and K2 stations, the variation in contamination according to the seasons, the dilferent routes of contamination, namely through water or by the trophic chaîn (periphfion and Spirogyra).The degree of contamination in M. praemona is signifïcatively higher at the Kl station, with the following ranking: Zn> Cu> Cd (fig. 2, 3 and 4). Compared with other literature data: FORSTNER et al., 1981; RADA, 1985; COSSON, 1987; PIP, 1992, the upper concentrations are the highest.The metal concentrations increase from winter to su...
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