Authorities fear sulphuric acid has leaked from a derailed freight train near the town of Julia Creek in north-west Queensland into a nearby waterway.
For almost three days, emergency services have been trying to reach the site near Julia Creek where the train carrying more than 800,000 litres of sulphuric acid derailed.
Police said it was possible 31,500 litres of the acid leaked from the train after it derailed 20 kilometres east of the outback town on Sunday.
Results from scientific testing up to eight kilometres downstream has raised concerns about the acidity levels in Horse Creek.
Queensland Police said the Department of Environment and Heritage Protection (DEHP) had advised there was an emerging concern about an increased adverse impact on the creek.
Wet weather continues to hamper efforts by emergency authorities to access the site.
Inspector Trevor Kidd from the Mount Isa Police said DEHP authorities were looking at strategies to neutralise the acid.
“The PH levels are changing there – that’s the information from their scientific people there, so that’s obviously a concern,” he said.
“That’s changed from early this morning when we were receiving briefings.
“We’ll continue to monitor that with all the relevant experts there.
“We’re treating it as a priority to get access to that site and put the right strategies into place.
“To the level of what that means, that’s obviously the department’s area of expertise.
“So that fact that there’s been a change, I think that is really the main issue – it’s changed from earlier.
“The strategy is how to neutralise some of that water around that area.”
Drones used to map crash site
Police said drones and other technology were being used to help with access, monitoring and mapping of the crash site.
Current access for salvage crews to Julia Creek was by vehicle from Mount Isa to Cloncurry and helicopter to Julia Creek.
Police said the Flinders Highway remained closed in both directions between Julia Creek and Richmond.
They said the two-kilometre exclusion zone would be in place for least another 48 hours.
The sulphuric acid had been bought by Incitec Pivot Limited (IPL) as an essential ingredient in fertiliser manufacture at its plant at Phosphate Hill, south of Mount Isa, a company spokesperson said.
The company said the sulphuric acid was used in the manufacturing process for ammonium phosphate fertilisers at that IPL plant, and was a regular purchase for that operation.
It said the majority of those fertilisers were supplied to farmers on the east coast of Australia.