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Pesticides in the Great Barrier Reef: Monitoring Tools

Pesticide runoff from agricultural applications poses a potential threat to water quality in the world heritage listed Great Barrier Reef (GBR) and sensitive monitoring tools are needed to facilitate effective monitoring of these pollutants. This thesis has worked to advance passive sampling tools for monitoring trace organic pollutants and their potential impacts on the GBR. The suitability of several available passive sampling tools for detecting trace concentrations of target pesticide analytes was investigated in a laboratory calibration chamber before experiments were conducted to further understanding of the response of Chemcatcher passive samplers in environmental conditions likely to be experienced in the GBR. Passive samplers were deployed in a survey of pesticides in the GBR environment and extracts were applied in bioassays to investigate their application for predicting mixture toxicity to GBR biota. When employed and interpreted appropriately, passive sampling tools have been shown to provide for sensitive and reproducible detection of organic pollutants in relatively pristine environments. While considerable research has been conducted into the performance and theory of analyte uptake by a range of passive sampling devices, several key knowledge gaps existed and were addressed in this study. The applicability of the performance reference compound (PRC) concept as an in situ calibration method for passive samplers using Empore Disk sampling phases (Chemcatchers) to monitor polar compounds was investigated. This experiment showed that while uptake of pesticides was linear and reproducible, PRC loss was not linear, meaning that the dissipation rates of these PRCs cannot be used to estimate the effect of field exposure conditions on uptake rates. An alternative in situ calibration technique using PRC loaded polydimethylsiloxane (PDMS) disks deployed alongside the Chemcatchers as a surrogate calibration phase has been tested and shows promise for future applications. Pesticide concentrations in waters flowing to the GBR have been shown to undergo dramatic fluctuations over short time periods and the potential for these conditions to limit the integrative period of sampling was investigated by simulating a changing concentration event in a calibration chamber. The ability for samplers to predict average concentrations was dependant on the deployment configuration (with or without membrane) used and the period of deployment relative to the changing concentration event. Passive samplers were employed in a survey of pesticides in GBR waters during a wet and dry season at river mouths, two nearshore regions and an offshore region. The nearshore marine environment was shown to be contaminated with pesticides in both the dry and wet seasons (average water concentrations of 1.3-3.8 ng L-1 and 2.2-6.4 ng L-1, respectively), while no pesticides were detected further offshore. Continuous monitoring of two rivers over 13 months showed waters flowing to the GBR were contaminated with herbicides (diuron, atrazine, hexazinone) year round, with highest average concentrations present during summer months (350 ng L-1). The use of passive samplers has enabled identification of insecticides in GBR waters which have not been reported in the literature previously. Extracts from passive samplers deployed at three sites in the GBR were applied to bioassays targeting integral life stages or functions of coral reef biota: scleractinian coral larvae, sea urchin larvae, a marine diatom and marine bacteria. The results demonstrate the utility of pairing passive sampling with bioassays and reveal that mixtures of organic pollutants in the GBR have the potential to cause detrimental effects to coral reef biota. This research outlines an approach that reduces one of the levels of simplification of risk assessment of pollutants to ecosystems by incorporating mixtures of chemicals present in the environment. The use of passive sampler extracts in toxicity testing allows pollutant mixtures to be assessed at a range of enrichment factors and, with the inclusion of biota from the ecosystem of concern, improves the relevance of results for predicting real world effects. The findings of this thesis are intended to be used to improve the application of passive sampling tools for routine monitoring to provide managers with understanding of the pesticides present, the potential effects of those pollutant mixtures and feedback on the efficacy of implemented land management practices in halting and reversing the impacts of pesticides on the GBR.