CONTAMINATION OF A DREDGED-MATERIAL DISPOSAL SITE (LA-ROCHELLE BAY, FRANCE) - THE USE OF THE ACETYLCHOLINESTERASE ACTIVITY OF MYTILUS-EDULIS (L.) AS A BIOMARKER OF PESTICIDES - THE NEED FOR A CRITICAL APPROACH

A single aspect of the toxic impact of a dredged material disposal sit e located near a mussel-farming zone was followed for eight months. Ac etylcholinesterase activity (AChE) of Mytilus edulis was investigated as a biomarker for possible contamination by neurotoxic compounds (car bamates and/or organophosphorous pesticides). Our observations showed that the enzymatic activities (including AChE) of these harbour mussel s were decreased in sites directly and indirectly influenced (accordin g to hydrodynamic conditions) by the dumping of dredged sediments, sug gesting possible contamination by pesticides. The strong correlations observed between AChE activity and growth parameters (length and weigh t) seems to show, however, that the enzyme activity is also indirectly controlled through growth restriction, which may imply limitation of the development of the nervous system in juveniles. The concentration of total proteins, as well as the spawning process also seem to distur b the assessment of AChE activity. These field observations clearly in dicate that the use of this enzyme activity as a biomarker should proc eed with caution. For example, the seasonal variability of such activi ty should be taken into account in a biomonitoring programme.