Evaluating Contaminant Levels in South Eastern Delphinids of Australia: Insights into the Toxicant Threats for the Burrunan Dolphin (Tursiops australis)
Creators: name: Foord, Chantel
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 410201
subject: Bioavailability and ecotoxicology
classificationCode: 410404
subject: Environmental management
classificationCode: 410402
subject: Environmental assessment and monitoring

description: Marine mammals, including dolphins, play a crucial role as sentinel species for monitoring the health of ecosystems, particularly in relation to toxicant accumulation. Due to their long lifespans, high trophic positions, and ability to store toxicants in their lipid-rich tissues, dolphins provide valuable insights into the types of pollutants entering marine environments and the potential impacts on biological systems. This thesis is the first study to provide a comprehensive assessment of toxicant body burdens in stranded dolphins from the south-east of Australia. It focuses on identifying the body burdens of per- and polyfluoroalkyl substances (PFAS), trace metals, and lipophilic organic pollutants, such as polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDT), resident dolphins found in south-east Australia, providing an understanding of toxicant dynamics across species, populations, and individuals.
The aims of this thesis were primarily to investigate relevant tissue samples for PFAS, PCBs, DDT and trace metals across three dolphin species within the region; the Burrunan dolphin (Tursiops australis), common bottlenose dolphin (T. truncatus), and the short-beaked common dolphin (Delphinus delphis). Further, to establish demographic, geographic and temporal trends in toxicant accumulation. Within the region the three species fill different niches with the Burrunan dolphin having just two small, isolated populations with high site fidelity to in inshore waterways, whereas the common bottlenose dolphin and short-beaked common dolphin have almost global distribution and locally inhabit primarily oceanic off-shore or coastal waters. Using the results, the threat to each population was assessed against known health thresholds. Each population was then evaluated against previous studies in Australia and placed in a global context for contaminant accumulation in Cetacea. This thesis had a particular focus on the Burrunan dolphin, a critically endangered species, endemic to the region, described in 2011, with limited prior toxicological knowledge. The suitability of remote biopsy sampling of live Burrunan dolphin individuals was investigated for future toxicant assessments by analysing the potential stratification within the blubber layer for PCBs, DDT and trace elements and the correlation to internal tissues between skin and blubber for trace elements. Finally, this thesis also explores Australia’s historical and current use of toxicants, and the current toxicant management in the context of the results found, and overseas practices. 
The findings revealed significant geographic and species-specific differences in toxicant body burdens, with the Burrunan dolphin demonstrating elevated body burdens when compared to the oceanic species (the common bottlenose dolphin and short-beaked common dolphin). This was particularly evident for PFAS, where the resident Burrunan dolphins were found to have 10 to 100 times higher PFAS levels in their liver compared to oceanic dolphins. Similar, but less pronounced, patterns were observed for the legacy Persistent Organic Pollutants (POPs) PCBs and DDTs. Trace metal accumulation, particularly for mercury (Hg), showed a different trend, with both inshore and offshore (oceanic) dolphin species displaying elevated concentrations, suggesting diverse sources of contamination. These variations are likely driven by habitat-specific factors, such as proximity to pollution sources and differences in dietary exposure.
This thesis placed the toxicant threat to south-east Australia's dolphin populations in a global context by evaluating contaminant levels against body burdens in dolphins from other regions. Further, comparing burdens to previously reported marine mammal toxicological thresholds, linked to health effects. The two Burrunan dolphin populations represented in the dataset have the highest reported global population concentrations of hepatic Σ25PFAS (Port Phillip Bay median 9,750 ng/g ww, n = 3, and Gippsland Lakes median 3,560 ng/g ww, n = 8), and included in the results is the highest reported individual Σ25PFAS (19,500 ng/g ww) and perfluorooctane sulfonate (PFOS, 18,700 ng/g ww) concentrations, at almost 30 % higher than any other Cetacea reported globally. Elevated hepatic Hg was found in Burrunan (62.5 – 4,990 mg/kg dw) and common bottlenose dolphins (102 – 1,770 mg/kg dw), also among the highest reported globally for dolphins. Individuals from all populations studied exceeded at least one critical health threshold for either PFOS, Hg, PCBs, and DDT, with some exceeding multiple investigated thresholds. This was particularly true for the Burrunan dolphin where three individuals exceeded all five thresholds, five exceeded three thresholds, eight exceeded two, and two exceeded one threshold, with only one individual remaining below all health thresholds. The widespread exceedance of these thresholds in a critically endangered species underscores the significant risks posed by toxicant exposure and the urgent need for effective conservation measures.
Demographic factors, including age and sex, also influenced toxicant accumulation. For example, while lipophilic contaminants like PCBs and DDT tended to increase with age due to bioaccumulation, PFAS levels were found to be higher in juvenile Burrunan dolphins than in adults. This pattern is likely due to metabolic differences, with adults potentially having greater capacity for PFAS excretion, maternal transfer, and growth dilution. Additionally, the thesis highlighted the correlation between toxicant levels and body length for non-essential trace elements such as arsenic (As), cadmium (Cd), and Hg.
A key aim of this research was to assess the suitability of remote biopsy sampling for monitoring contaminants in the Burrunan dolphin. Results indicated that remote biopsies could be effectively used to determine levels of trace elements, PCBs, and DDT, with the blubber portion providing a more reliable reflection of internal tissue concentrations than skin. Although stratification was observed for some contaminants, e.g., PCBs, copper (Cu), selenium (Se), manganese (Mn), and zinc (Zn), no stratification was found for total ΣDDT, As, Cd or Hg, indicating that blubber samples could provide valuable insights into contaminant body burdens.
Lastly, the findings highlighted potential regulatory gaps in Australia's toxicant management, particularly in relation to Hg and PFAS. Inconsistencies between state-level Hg regulations and global treaties have contributed to elevated contamination levels in the aquatic environments studied. Moreover, Australia's higher trigger values for toxicants compared to other industrialised nations raise concerns about the adequacy of current regulations in protecting marine species. This research calls for enhanced monitoring, stricter regulations, and further investigation into the sources and pathways of contaminants in Australian waters, particularly in the inshore habitats of the critically endangered Burrunan dolphin.