ABSTRACT The tropical and subtropical nearshore marine environments of Queensland, Australia sustain diverse and unique marine wildlife. Continuous population growth and land-use changes along the Queensland coastline are known to exert numerous anthropogenic pressures on these marine ecosystems, including the delivery of high sediment loads. Sediments also provide a transport pathway for persistent organic pollutants (POPs) from rural and urban catchments into the marine environment. While such pollutants are known to be elevated in marine sediment and biota from nearshore areas in Queensland, their input and distribution pathways, as well as exposure and associated risks to wildlife populations are only partially understood. Mounting evidence suggests that POPs may contribute to population declines in marine wildlife species; however, limited information is available regarding the accumulation and effects of these contaminants in endangered or threatened marine turtles. This study aimed to redress some of these information gaps using a case study approach in marine turtle habitats of Moreton Bay, and other embayments in Queensland. Among persistent organic pollutants (POPs), dioxins (polychlorinated dibenzo-p-dioxins; PCDDs) and to some extent also dioxin-like PCBs (polychlorinated biphenyls; PCBs) were found to be widespread and often present at elevated (ppb) levels in surface sediments from Moreton Bay. However, while PCDD/F toxic equivalencies (TEQs) are above international (Canadian) sediment quality guidelines at numerous sites in Moreton Bay, in general TEQs across the Bay are relatively low compared to those from contaminated locations near dense industrial activities. POP contamination in surface sediments across Moreton Bay was investigated by a combination of GIS spatial mapping, geostatistical and traditional statistical modalities. High spatial variability and complex spatial distribution patterns were revealed. High resolution GIS kriging model outputs from the mid to southern Bay facilitated identification of distinct sediment contamination zones, with highest PCB and PCDD/F levels present in nearshore locations, associated with nearby river systems. While primarily governed by organic carbon, a multitude of physical, chemical and hydrological factors were identified to influence the spatial variance of PCDD/F concentrations. The main parameters governing PCDD/F spatial distribution were identified as sediment geochemistry, water depth and anthropogenic alterations of the physical environment and, together, all quantifiable explanatory variables (including hydrodynamic flushing) explained ≈75% of spatial PCDD/F variance. Together, the interaction of these parameters results in complex distribution patterns and highly variable concentrations even among neighbouring sites of 1-3 km resolution. These results suggest that prediction models of POP distributions in the nearshore marine environment may require high-resolution validation, and highlights that the design of low resolution monitoring strategies can have profound impacts on the reliability of contaminant information or any subsequent extrapolations. This knowledge and methodology can be utilised to optimise on-going and future near-shore sediment monitoring programs both locally and in other regions around the world. Using the spatial distributions of dioxin-like contaminants within sediments, this study provided an opportunity to assess field-based relationships between habitat contamination and local marine biota contamination. Detectable levels of PCDD/Fs and dioxin-like PCBs were measured in all green, hawksbill, loggerhead and flatback marine turtle tissues. POP concentrations in sediments were found to significantly correlate with those in the herbivorous green turtle from different sediment contamination zones. These findings demonstrate that sediments represent an important secondary contaminant source and lead to redistribution of POPs to the marine food chain. POP concentrations and TEQs clearly increased from sediment to turtles as well as with increasing trophic levels in marine turtle species. The results from this study demonstrate that the extent of sediment contamination within foraging habitats governs marine turtle exposure, while, trophic status and to some extent age influence contaminant exposure within a particular contamination zone. Despite the relatively low TEQ in sediments from Moreton Bay, TEQ levels in green turtle sub-populations foraging from near-shore locations and higher trophic loggerhead and flatback turtles are similar or elevated compared to those reported for other marine wildlife from Moreton Bay and elsewhere, even compared to higher trophic species from locations impacted by dense industrial activities. High bioaccumulation potential of 2,3,7,8-PCDD/F and dioxin-like PCBs compounds were estimated for green turtles using biota to sediment accumulation factors. Selective accumulation of toxicologically more potent (i.e. lower chlorinated) PCDD/Fs was observed for higher trophic marine turtles, resulting in increasing TEQs for the carnivorous species. Biomagnification was also observed for some non-2,3,7,8-substituted dioxin congeners which typically do not accumulate in most biota. These results are proposed to be due to relatively high accumulation efficiency and/or low metabolic capacity for these POP compounds in marine turtles. These findings are also hypothesised to reflect temperature dependant, greater bioavailability of hydrophobic chemicals in sub-tropical and shallow marine systems. An additional pilot study revealed that in contrast to PCDD/Fs and PCBs, levels of persistent flame retardants (polybrominated diphenyl ethers; PBDEs) were relatively low in marine turtles and other marine species (dugong, fish and shellfish) from Moreton Bay. This suggests relatively low level input of these more recent industrial products into the marine environment. However, as elevated levels of PBDEs have been reported in blood from the general population of Australia, ongoing transport from the terrestrial to the marine system and redistribution of these contaminants, similar to PCDD/F and PCBs, would be expected to occur into the future. Limited information is available regarding the sensitivity of reptiles to and effects of POPs, however, studies have shown that reptiles are sensitive to POPs albeit with uncharacterised relative potency. In the absence of robust toxicological information for reptiles or marine turtles, the potential risks associated with PCDD/F and PCB exposure of Queensland turtle populations was evaluated using toxicity for sensitive biological endpoints observed in mammals and birds. Using probabilistic methodology for marine turtles from Queensland, the body burden of up to 31% and 55% of green and loggerhead turtles, respectively, are above the threshold levels where the most sensitive physiological effects are observed in mammals and birds. While this evaluation illustrates that the contaminants investigated have the potential to impact on the health of marine turtle populations, it must be highlighted that it is compromised by the lack of species-specific (and in this case, class-specific) information, the uncertainty of which is often considered to represent a factor of at least 10. The findings of the present study indicate that exposure to POPs has the potential to adversely affect the health of Queensland’s marine turtle populations, and highlight the need for robust information on reptile specific sensitivity to these compounds.
| Identifer | oai:union.ndltd.org:ADTP/279262 |
| Creators | Siobhan Hermanussen |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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