In the “Scammell Report”, Environmental Problems Georges Bay, Tasmania , it was hypothesised that a toxic compound killed the oysters in Georges Bay following a flood in January 2004.
It was further hypothesised that fresh water delivered that compound to the oysters during the flood event.
It was hypothesised that the compound floats and was a man made chemical used in the catchment. Further, this compound was being increasingly used and was therefore associated with a growth industry in the catchment.
Is a toxic agent present or absent
The “Scammell Report” called for an immediate investigation, but that has not been forthcoming.
In January of this year the authors of the “Scammell Report” decided to instigate a toxicity testing program in the George River catchment. The value of toxicity testing is that the instigator does not need prior knowledge of what chemicals are in use in the catchment.
The test simply answers the question is a toxic agent present or absent.
Given that oyster mortality occurs after rainfall events it was believed that the toxic agent would most likely be present during the first flush of rainfall events.
Accordingly the authors first set out to establish that the surface layer was not carrying a toxin during dry weather flow. In mid January surface water concentrating devices were deployed at three locations in the George River catchment.
These locations were:
1. The South George River, upstream of dairy farms and downstream of a timber plantations (South George),
2. The George River just downstream of the confluence of the North and South George, adjacent to dairy farms (George River),
3. George River one kilometre upstream of the town water uptake pipe (Upstream).
Sampling was undertaken on the 17th of January following three weeks of dry weather. The purpose of this sampling was to establish a baseline survey to demonstrate that the surface waters are typically harmless to test organisms.
In addition to the above three locations a grab sample was also collected from the North George River.
The test organisms were oyster larvae and sea urchin larvae. Oysters are relevant to the observed mortality of oysters and sea urchins would give some information to establish if the problem was oyster specific or capable of affecting other species.
Toxicity testing was initiated on the 18th of January at a commercial Sydney Laboratory.
Results of that testing follow in:
These unexpected results were immediately dispatched to Tasmanian Health and it was agreed that the testing would be repeated.
It was agreed that re-sampling would occur on the 14th of February and that scientists from DPIWE would also collect samples.
A scientist was sent from the Sydney Testing laboratory to collect the samples from the George River catchment.
An additional test animal was included in the next round of tests. This additional animal was the water flea (Ceriodaphnia duba), a freshwater filter-feeding crustacean.
The Government is yet to release their findings
Additionally a surface sample collection devise was deployed in the North George River. Three hours prior to sampling it was discovered that the sampling devices in the North and South George Rivers had been interfered with. Both were redeployed, however, the collection devices were normally left in place for 48 hours prior to sampling.
Thus, the samples from the North and South George Rivers are not comparable to the two downstream sites.
In discussion with the DPIWE scientist it was made clear that they would be running the 48-hour toxicity test on the water flea so that they could independently confirm our findings. Table 2 lists the findings from this round of toxicity testing.
An additional sample from Crystal Creek was sent to the Sydney Testing facility on the 15th; however, this sample failed Chain of Custody documentation and was therefore deemed non-defendable, i.e. the integrity of the sample cannot be guaranteed.
Results from the second round of testing were completed on the 18th of February.
The government is yet to release their findings.