A SEVERE marine pollutant that may have been released into Gladstone Harbour during the Western Basin dredging project went unassessed before dredging began, due to failures in the sediment testing program for the project.
The Gladstone Ports Corporation failed to test for the pollutant despite recommendations provided in 2009 that harbour sediments be "immediately" tested for the substance.
That failure was allowed to occur due to a weakness in the National Assessment Guidelines for Dredging; CSIRO scientist Dr Graeme Batley - a key contributor to the guidelines - has confirmed.
The pollutant, dibutyltin (DBT), is the breakdown product of the toxic chemical tributyltin (TBT), a key ingredient in anti-fouling paints that was banned in 2008, which was a known "contaminant of concern" in the harbour.
These substances were also overlooked during investigations into a 2011 fish disease outbreak in the harbour that coincided with the dredging project.
While a GPC spokeswoman said the dredged sediment was deemed suitable for "its intended disposal location", she referred all questions to documents "available on the project website".
Those documents show sediment was dredged from an area "of concern" for potential DBT contamination, near the RG Tanna coal terminal, in the months preceding the 2011 harbour closure.
But the documents did not specify where the sediment was dumped; an issue the port did not clarify.
A 2009 study on the chemicals' effects on molluscs in the harbour found DBT was more prevalent than TBT and the "major effects to biota" were likely caused by butyltin compounds in the sediment, including DBT, rather than directly from vessels using the banned paint.
That study recommended "immediate" sediment testing for all such compounds "to ascertain potential for contamination and re-suspension".
While the tests completed found little evidence of TBT, the port's environmental impact statement shows no tests were completed for the key pollutants DBT or monobutyltin (MBT).
CSIRO chief research scientist Dr Graeme Batley, who contributed to the guidelines, said while TBT was more toxic, "normally if you were doing an investigation, you would test for all the breakdown substances".
"The main reason for (testing for) TBT is it's more toxic, DBT and MBT are still toxic, but not to the same extent," he said.
"But DBT certainly lasts longer than TBT - in sediment you'll see DBT and MBT present for many years after it's broken down.
"The toxicity is probably the main reason why it's not in the guidelines; but normally, the analytical labs will probably give you the information anyway."
The federal Department of the Environment has to date declined to investigate the matter.The chemical:
Dibutyltin (DBT) is a "severe marine pollutant" and the initial breakdown product of a highly toxic chemical, tributyltin (TBT), an ingredient in anti-fouling paints that was banned worldwide in 2008.
TBT breaks down into DBT in sediments over several years, with DBT staying dormant in sediments, if left undisturbed, before it breaks down further into monobutyltin (MBT) and finally tin.GPC's response:
"Material to be dredged for the Western Basin Dredging and Disposal Project (WBDDP) was extensively sampled and analysed prior to dredging and all material was assessed to be suitable for its intended disposal location.
"An extensive campaign of geotechnical testing within the dredging footprint was carried out as part of the Environmental Impact Statement (EIS).
"The results of these sediment studies indicated that there were no exceedences of contaminants, with the exception of some metals, which were identified as naturally occurring within Port Curtis.
"Documents detailing the approved areas for onshore and offshore placement of dredge materials are available on the project website, www.westernbasinportdevelopment.com.au "
Correction: CSIRO's Dr Graeme Batley did not provide any comment specifically concerning Gladstone Harbour with relation to the National Assessment Guidelines for Dredging. Dr Batley said he would not consider DBT a severe marine pollutant.