Scientists probe connection between deadly frog disease and coal wastewater

Frogs in Australia's oldest national park have higher rates of a deadly fungus when exposed to wastewater from a coalmine compared to unexposed waterways, a study suggests.

The study, published in the Journal of Hazardous Materials Advances last month, looked at chytrid fungus levels in two species of frog in Royal National Park, downstream from the Metropolitan Mine, south of Sydney.

Lead author Shannon Kaiser, an ecotoxicologist from Macquarie University, said the wastewater from the mine could not definitively be identified as the cause of the observed disease pattern.

"However, the association is concerning and suggests pollution and wildlife disease risk may interact in freshwater ecosystems,"

he said.

Mr Kaiser said water quality monitoring programs should be expanded to reflect the potential disease risk to animals from environmental changes.

Typically water monitoring measures things like pollution, temperature and oxygen.

"Our results suggest biological effects, including frog health and pathogen loads, should also be considered," Mr Kaiser said.

In response, a spokesperson for Peabody, the mine's operator, said any causal link between water chemistry changes and frog infection intensity described in the study was speculative.

The study was undertaken between December 2022 and February 2023, a few months after unlicensed discharges of coal contaminated water from Metropolitan Mine overflowed into Camp Gully Creek. 

The NSW Environment Protection Authority fined the mine's operator, Peabody, more than $500,000 and issued clean-up orders along with new regulatory conditions after the incident.

The Peabody spokesperson said it had invested more than $1.5 million in upgrades since 2022 to reduce discharge risk.

"Including expanded water storage capacity and [Metropolitan Mine] now publishes real-time water quality data on its website covering some of the parameters examined in the study," they said.

"Metropolitan separately funds a three-year program in the Royal National Park to support rehabilitation of the southern stuttering frog, a species affected by chytrid fungus."

What happened to the frogs?

Cooper Riach, from Sutherland Shire Environment Centre, raised concerns about frog health after seeing the coal waste enter Camp Gully Creek in 2022.

"You could put your hand into the water and just swish your hand around a bit and all this oily, thick, viscous substance would come off the base of the creek," he said.

"We came across a little green frog, which had unfortunately gotten caught up in all this, and it had just got covered in this coal waste."

Mr Kaiser saw a photo of the frog and decided to study how exposure to wastewater might impact adult amphibian body condition, immunity, and disease outcomes.

Frogs were sampled from sites both exposed and unexposed to wastewater discharge from the coalmine.

Unexposed sites included other tributary creeks to the Hacking River, and points on the river before the mine.

There were 166 frogs found across 25 unexposed sites, and 180 frogs from 22 exposed sites.

Most of these frogs were either the leaf green tree frog (Dryopsophus phyllochrous) or the Stony Creek frog (Rhyaconastes lesueurii).

Forty-five of the frogs were swabbed to see if they had the chytrid fungus, which can infect their skin.

"Because frogs rely on their skin to regulate water and salts, heavy infections can cause the disease chytridiomycosis, which can be fatal," Mr Kaiser said.

Eighteen frogs tested positive for the fungus across both exposed and unexposed sites.

Leaf green frogs in exposed sites were more severely infected compared to unexposed sites.

"[Leaf green] frogs in exposed streams carried higher disease load," Mr Kaiser said.

"It dictates whether an infection remains harmless or becomes fatal. A frog can be infected, but not be lethally impacted."

Leaf green frogs that were dead or showing signs of late-stage chytridiomycosis were only found in exposed sites.

But the infection intensity did not differ greatly between exposed and unexposed sites for the Stony Creek frog.

The overall number of frogs across both species and their body condition did not differ significantly between sites downstream of the mine and areas that did not receive wastewater.

Could something else influence frog disease?

Mr Kaiser said there could be other reasons the frogs had an increased transmission rate of chytrid in tested exposure sites.

Most of the exposed sites were in the Hacking River where having a higher density of frogs, compared to smaller creek areas, could influence fungus spread.

"It could be that something else is entering that stream that we're not aware of from further upstream from beyond the coalmine," he said.

An EPA spokesperson said it received the frog study and acknowledged the value of emerging environmental research for understanding potential impacts from mine discharges.

They said it had recently required the mine to engage independent experts to undertake macroinvertebrate monitoring in Camp Gully Creek.

"The EPA is currently reviewing the monitoring results to determine whether any further studies or actions are necessary," the EPA spokesperson said.