Immunomodulation in blue mussels (Mytilus edulis) exposed to a pulp and paper mill effluent in Eastern Canada

Abstract

Blue mussels (Mytilus edulis) were caged at three sites situated at increasing distance from the point of discharge of a pulp and paper mill effluent from July to October 1998. Two additional cages were deployed: one inside and one at the mouth of the adjacent industrialized Pictou Harbour. After 90 d exposure, we measured growth, survival, haemocyte counts (HC), phagocytic activity (PA), lysosome retention (LR) and bacterial clearance (BC). There was a small but significant difference in growth between cages. Mussels closest to the mill effluent grew the most while those at the mouth of the harbour grew the least. Mussels from three cages showed similar difficulty in clearing bacteria; the cage inside the harbour, the cage nearest to the pulp mill effluent and the cage furthest from the pulp mill, receiving a mixture of both pulp mill and harbour effluents. The mussels from those cages also showed the highest heavy metal burdens and conversely, the cage showing the most rapid clearance, outside both effluents, also showed the lowest heavy metal burden. Mussels caged in the pulp mill effluent showed lower PA and LR and higher mortality during the bacterial clearance test than other mussels. These results suggest that immunological biomarkers might be a useful and more sensitive adjunct to endpoints presently being measured from caged bivalves in environmental effects monitoring (EEM) programs, and assessments of aquatic environmental quality.