نبذة مختصرة : Field biomonitoring based on molecular biomarkers detects early warning signals of stress suffered by organisms exposed to contamination. The lower part of the Ebro River basin has a long pollution history related to the presence of a chlor-alkali plant adjacent to Flix. In addition, the Ebro River has been affected by the invasion of alien species that damage its natural ecosystem. In this thesis, Cyprinus carpio (common carp) an Dreissena polymorpha (zebra mussel) were used as a model species in laboratory and field studies intended to the development of a multimolecular biomarker approach to identify the most relevantly effects of pollutants in the field. Gene expression techniques were used to study specific physiological defensive mechanism. The application and improvement of a well-established markers in different aquatic species and following different approaches allowed to analyze modes of action and to outline effects of persistent organic and inorganic pollutants found in the field. The results showed that chronic exposure to mercury of common carp results in increased levels of metallothionein in kidney, in scales (albeit at lower extent), but not in liver, considered as the primary detoxification organ. The measure of gene expression in scales provides the possibility of a new non-lethal method of study. Studies of toxicant effects in zebra mussel revealed that this bivalve could be used as potential sentinel specie for freshwater monitoring. Analysis of its detoxicfication mechanisms, and particularly of its ABC membrane transporters in adult and the early life stages could help understanding the survival of this species in highly contaminated areas.
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