Sub-lethal stress to oysters caused by resuspended contaminated sediments

Abstract

Resuspended contaminated sediments represent an important route of contaminant exposure for aquatic organisms. Filter-feeding organisms are exposed to contaminants both in the dissolved (at the gills) and particulate form (in the digestive system) during resuspension events. In addition, these organisms must manage the physical stress associated with an increase in total suspended solids (TSS). To date, few studies have attempted to distinguish the contributions of these factors to biological effects associated with resuspended contaminated sediments. We mixed field-collected sediments (<63 μm) from clean and contaminated field sites to create four treatments of increasing metal concentrations. Sydney rock oysters were then exposed to sediment treatments at different TSS concentrations for 4 days, and cellular biomarkers (lysosomal membrane stability, lipid peroxidation and glutathione) were measured to evaluate sub-lethal toxicity. Biomarker responses were assessed against metal concentrations in dissolved and particulate phases to establish causal relationships. Lysosomal membrane stability was the most sensitive biomarker for distinguishing effects from resuspended contaminated sediments, as increasing amounts of contaminated TSS increased lysosomal membrane destabilisation. Antioxidant status appeared to be sensitive to TSS alone, potentially serving as a sensitive indicator of sediment effects independent of contaminants. Our results illustrate the importance of considering contaminant exposures from resuspended sediments when assessing the toxicity of contaminants to aquatic organisms, and the potential diagnostic value of a suite of biomarkers.

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