A report from Natural Heritage Trust (Coasts and Clean Seas) Project No 25425
Department of the Environment and Heritage
- TBT analysis protocol development and current contamination assessment (PDF - 257 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 1 (PDF - 353 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 2 (PDF - 270 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 3 (PDF - 293 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 4 (PDF - 20 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 5 (PDF - 61 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 6 (PDF - 16 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 7 (PDF - 31 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 7a Victoria (PDF - 16 KB)
- TBT analysis protocol development and current contamination assessment - Appendix 7b NSW - ZIP (PDF - 14,372 KB)
The use of tributyltin-based paints as antifoulants on vessel hulls in Australia has been restricted since 1989, due to worldwide problems of contamination and impacts on shellfish populations in areas near harbours and shipping lanes. However no systematic study has quantified changes in levels of TBT contamination in Australia since the introduction of the restrictions.
Regulatory authorities face a problem in addressing TBT-related issues such as the disposal of dredge spoil from contaminated areas because of unreliability and high variance in the results from laboratory analysis of TBT-contaminated marine sediments.
This study, conducted over 2000 to 2003, involved two phases. The first phase was an interlaboratory trial to assess whether the high-variance problem was attributable to sample handling and analytical methods used by laboratories. The second phase was to field test a sampling protocol based on tiered levels of composites. This was designed to reduce high variance attributed to the heterogeneity of TBT contamination, for example TBT associated with paint flakes or other particulate matter. Such a field sampling program would enable the reliable benchmarking of TBT-contaminated sites in each Australian State and Territory. Such sites could be revisited at a future date to assess long term trends in levels of TBT contamination.
The interlaboratory trial showed that poor performance in TBT analysis was not related to the method of analysis used, but rather the competence of the laboratory with their method of choice. Where laboratory performance is satisfactory, inter-sample variation seemed not to be an artefact of analytical uncertainty.
It is recommended that criteria for TBT analysis need to be set, so that laboratories can ensure that their methods meet these criteria and include limits of detection that meet environmental guidelines used by regulatory agencies.
The quality of historical data relating to TBT in Australian sediments is scant and of limited value for assessing trends over time. Most of the available data relates to pre-dredging assessment of shipping channels and harbours. Such data almost invariably comprises mean concentrations from cores through the accumulated sediment thickness to be dredged, thus masking concentrations near the surface - which are most relevant to the exposure of biota to TBT. In addition, regularly dredged areas are often not representative of the undredged areas that are certainly larger in extent and more relevant to the exposure of biota to TBT contamination.
The field sampling strategy used in this study benchmarked a number of TBT-contaminated reference sites that could be used for future reassessment to gauge changes over time, for example in relation to changing TBT-based antifoulant usage patterns. However, the sampling protocol was not successful in reducing variance in TBT concentration data for sediments that may have high heterogeneity of particulate TBT. Even intensive compositing of samples (e.g. 25 to 50 cores per composite sample) did not consistently reduce variability in data relating to TBT concentrations in sediments, and variability in TBT concentration data remained greater than for all other analytes used in this study to characterize sediment quality.
Analytical results from subsamples of well-mixed composites each comprising 50 sediment cores sometimes had high variability in TBT concentrations (coefficients of variation approaching 90% in some cases), showing that in addition to high variability between composites, variance within composites was problematic.
Accordingly, on the basis of the findings from this study, in particular the high variance found in TBT-contaminated sediments despite a high level of confidence in laboratory analytical performance, multiple samples and/or replicates are needed to assess actual contaminant levels for comparison against sediment quality guideline limits, and the confidence limits applied to measured values need to be very broad.
During this study, the low levels of TBT contamination found at sites specifically chosen by state authorities for assessment in the study on the basis that the sites had a history of significant TBT contamination suggested that there is less extant TBT contamination in Australian waters - at least in recreational boating areas, since restrictions on TBT usage were introduced in 1989.
Authorship of the Report
This report was prepared by Dr Munro Mortimer,
Senior Principal Scientist, Water Sciences Unit,
Queensland Environmental Protection Agency,
80 Meiers Road, Indooroopilly, 4068.
It incorporates all amendments and additions made to an earlier draft by members of the Project Technical Review Committee.
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The views and opinions expressed in this publication are those of the authors and do not necessarily reflect those of the Australian Government or the Minister for the Environment and Heritage.
While reasonable efforts have been made to ensure that the contents of this publication are factually correct, the Australian Government does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication.