Abstract
Semi-volatile organic contaminants (SOCs) have the ability to undergo long-range atmospheric transport to remote ecosystems like Antarctica. Very little is known about current SOC trends in fish from the McMurdo Sound region of Antarctica, as well there are no fast and effective extraction methods to analyse multiple classes of contaminants in fish. Fish are important food sources and the emerald rock cod (Trematomus bernacchii) is considered a sentinel bio-indicator for monitoring changes in Antarctic ecosystem quality. This type of assessment is becoming a necessity especially as a recent study reported high polybrominated diphenyl ether (PBDE) concentrations in T. bernacchii in the vicinity of the McMurdo Station sewage outfall. Additionally, the potential impact of PBDEs on the fish physiology is unknown. This Ph.D. research describes the development of an extraction method for three classes of halogenated organic contaminants (current-use and legacy pesticides, PBDEs and polychlorinated biphenyls (PCBs)) that have SOC characteristics. The method was applied to measure spatial and temporal trends in two species of Antarctic fish from McMurdo Sound. Specific focus was given to changes in PBDE concentrations in fish from the vicinity of the McMurdo Station sewage outfall. This research also describes the physiological responses of T. bernacchii exposed to a mixture of PBDEs and suggests useful biomarkers for future eco-toxicology studies.
The developed high sample throughput selective-pressurised liquid extraction (S-PLE) minimises fat elution by using a fat retainer, Florisil, during extraction. The optimised parameters were: n-hexane:dichloromethane (75:25 v/v) as the extraction solvent, a 0.0078 fat-to-fat retainer ratio, three individual 5-min extractions with flush volumes of 150% and a selection of labelled surrogate standards (isotope-dilution) for analysis of SOCs by gas chromatography/mass spectrometry. SOC concentrations were measured in T. bernacchii and bald cod (Pagothenia borchgrevinki) collected at different locations and various years. A sub-chronic dose study was designed to measure the impacts of PBDEs on T. bernacchii. Two environmentally relevant concentrations of a PBDE mixture (BDE-28, BDE-47, BDE-100, BDE-99, BDE-154, BDE-154, BDE-183 and BDE-209) were administered fortnightly over 42 days and cellular changes, biotransformation and antioxidant defence responses were measured using biochemical, molecular and enzyme assays on Day-0, Day-14, Day-28, Day-42 and Day-56.
The mean PBDE concentration and PBDE profiles were similar in cryopelagic (P. borchgrevinki) and benthic (T. bernacchii) fish in the vicinity of McMurdo Station and were similar at different locations. The local research stations were contributing to the PBDE concentrations detected in fish from the vicinity of the McMurdo Station outfall. The sewage treatment upgrades did not change the PBDE burdens in fish. Temporal trends indicated that PBDE concentrations were increasing and the PCB concentrations were decreasing in the McMurdo Sound. PCB profiles in fish from the vicinity of the McMurdo Station indicated the presence of higher chlorinated PCBs while at the more remote site lower chlorinated PCBs were detected. This is the first study to measure current-use pesticides in Antarctica. Chlorpyrifos, trifluralin, and dacthal were detected in most Antarctic fish samples. Of the legacy pesticides, total hexachlorocyclohexane (HCH) dominated in all fish samples and the remaining legacy pesticides, as well as the current-use pesticides were both spatially and temporally variable. This study found that changing sea-ice condition may play a role in the variability in both current-use and legacy pesticide concentrations in Antarctic fish.
The changes in the total lipid content, lipid peroxide levels and protein carbonyl levels in the liver of T. bernacchii indicated that varying degrees of lipids and proteins changes had occurred in fish from the PBDE treated groups. Additionally, the glutathione-S-transferase (GST) activity reached peak activity faster than the ethoxyresorufin-O-deethylase (EROD), indirectly supporting the emerging hypothesis that the reductive debromination of PBDEs may be occurring. The present study indirectly demonstrated that metabolic activity and oxygen capacity was affected by exposure to increasing PBDE concentrations. Consequently, the balance between metabolic demands and aerobic capacity are essential for the survival of Antarctic fish, such that if metabolic demands and oxygen capacity is disrupted and if the animal is unable to return to basal metabolic rates and function within its aerobic capacity, it could possibly result in a sequence of events which may compromise growth performance. The future implication for wild T. bernacchii, in the vicinity of the sewage outfalls, to increasing PBDE concentrations, may be diminished growth performance and fecundity.
Some useful and informative biomarkers determined from the present study for PBDE-related impacts were: protein carbonyl and lipid peroxides for cellular level responses. GST may be a more suitable choice as an enzyme marker than EROD. Copper/zinc superoxide dismutase mRNA is not a suitable molecular marker for oxidative stress; catalase and glutathione peroxidase are more promising enzyme markers. It is recommended that the PBDE and current-use pesticides concentrations are continually monitored to assess ecosystem health and efforts into decreasing PBDE concentrations are made by considering changes to the current sewage treatment systems at the research stations.