Exposure-dose-response of Saccostrea glomerata (Sydney rock oyster) to cadmium obtained from suspended sediments and phytoplankton

Abstract

Estuaries can receive anthropogenic contamination from both land and ocean sources making estuaries susceptible to contaminants such as cadmium. A common inhabitant of Eastern Australia estuaries is the oyster, Saccostrea glomerata which is able to uptake cadmium through three pathways: 1) suspended sediments,2) water column, and/or 3) diet. In this study, Saccostrea glomerata were exposed to cadmium through cadmium-spiked suspended sediments (19 & 93 mg/kg) and cadmium-enriched phytoplankton (2-3 μg/g) under controlled laboratory conditions. Cadmium uptake and effect measurements, total antioxidant capacity, lipid peroxidation, and lysosomal stability were measured. The oyster tissue from the suspended sediments (SS) experiment accumulated cadmium from both treatments (Low-Cd SS; 2 -10 mg/kg & High-Cd SS,15-49 mg/kg). Some cadmium desorbed from the sediment within 6 days of the suspended sediments experiment. The oysters could have obtained cadmium both from the suspended sediments and the water column. Oysters accumulated less cadmium in the phytoplankton experiment with final tissue concentrations between 0.7 μg/g and 4.1 μg/g. In both experiments, cadmium-exposed oysters showed a significant reduction of total antioxidant capacity compared to the controls’ total antioxidant capacity. In the suspended sediments experiment, the Low-Cd SS treatment had a higher mean total antioxidant capacity of 18.0 ± 5 mM/mg protein compared to the High-Cd SS treatment of 14.0 ± 5 mM/mg protein. Oyster fed cadmium-enriched phytoplankton had a reduction in total antioxidant capacity with 18.0 ± 4 mM/mg protein. Comparison between both experiments with the cadmium-exposed oysters the total antioxidant capacity reduction was not significantly different between experiments. Thiobarbituric acid reactive substances, an oxidative damage assay, showed similar patterns. In the suspended sediments experiment the Low-Cd SS treatment had lower thiobarbituric acid reactive substances (93.0 ± 22 MDA nmol/mg protein) compared to the High-Cd SS treatment (139.0 ± 41 MDA nmol/mg protein). The thiobarbituric acid reactive substances for the phytoplankton experiment were 127.0 ± 11 MDA nmol/mg protein. In both experiments thiobarbituric acid reactive substances concentrations were similar. In both experiments, cadmium-exposed oysters had lysosomal destabilization percentages that were significantly higher than the controls’ percentages (Control averages: 34 ± 8% & 35 ± 9%). Lysosomal destabilization for the Low-Cd SS treatment was 38 ± 12% and 42 ± 9% for the High-Cd SS treatment. Lysosomal destabilization for the oysters fed cadmium-enriched phytoplankton was 46 ± 2 %. Comparison between both experiments showed that the lysosomal destabilization percentages were not significantly different between experiments. Saccostrea glomerata experienced oxidative stress and lysosomal destabilization from a low dose of cadmium derived from phytoplankton and experienced oxidative stress from cadmium ingestion via suspended sediments and the water column high cadmium concentrations. These results from both experiments support the hypothesis that Saccostrea glomerata can take cadmium up through suspended sediments and the water column and can cause oxidative stress and lysosomal destabilization. Results also showed that low concentrations of cadmium through phytoplankton (diet) can cause cadmium stress.

Date of Award	2013
Original language	English
Supervisor	Bill Maher (Supervisor) & Anne Taylor (Supervisor)