Scientists will study the bodies of 40 koalas that were euthanased due to poor health to work out whether their proximity to a Victorian aluminium smelter caused serious deformities.

A similar study done on kangaroos living near Alcoa's Portland aluminium plant more than a decade ago found that many of the animals had deformed bones and teeth as a result of fluorosis, a condition linked to the facility's fluoride emissions.

In September last year Portland Aluminium engaged an independent consultant to assess koala populations living in a 17-hectare blue gum plantation around the smelter.

Of the 114 koalas examined, 40 were found to be in such poor health that they were put down.

Seventy-four were returned to the area.

The females were subjected to fertility control measures.

'Severe bone growths'

University of Melbourne senior wildlife lecturer Jasmin Hufschmid is part of a team that has been commissioned to study the bodies of the koalas that were put down.

Dr Hufschmid was involved in the six-year study on kangaroos living near the plant that began in 2008.

"We found that the kangaroos did show signs of both dental, or teeth-affecting fluorosis, and skeletal, or bone-type, fluorosis," she said.

"For those within 100 or 200 metres from the point where the fluoride gets emitted from, those animals had quite severe impacts because they had quite severe bone growths.

"Those animals were in quite poor body condition and were probably uncomfortable due to the impacts as well."

She said because kangaroos can live for about 15 years, the fluoride accumulated in their bodies over time.

Uniform results

A subsequent study that looked at the effects on other animals, including wallabies, koalas and possums, returned findings consistent with the earlier research.

"When you have an excessive intake of fluoride, what happens is that the fluoride gets incorporated into mineralised tissue in your body," Dr Hufschmid said.

"The key mineralised tissues in your body are your teeth and your bones.

"If you're exposed to high levels of fluoride – we're not talking about what's in the groundwater or the water supply, we're talking about really high levels of fluoride – then that causes damage to your teeth.

Dr Hufschmid said discoloured, soft teeth – as well as issues with bone growths and joints – could result from long-term exposure to excessive fluoride.

She said fluoride occurred naturally in the Earth's crust, but some industrial processes also led to its emission.

"It includes coal-fired gas stations, ceramics manufacturing and also non-ferrous metal manufacturing like aluminium smelting as well," Dr Hufschmid said.

"As much of it as possible is usually filtered out, but a small portion can't be.

"What tends to happen with the aerial emission of fluoride is that some of it will drop down and settle on the ground.

Action taken, smelter says

The US-based Alcoa, which operates aluminium smelters around the world, said in a statement that the assessment of the population at Portland was prompted by a count in May 2020 that identified 170 koalas in the area and raised concerns about the density of the population.

"Data collected during the assessment is being analysed by the University of Melbourne to inform the development of a plan for the ongoing management of the koala population and areas they inhabit," the company said.

"This is expected to be completed in the coming months."

Alcoa said previous studies that focused on animals such as kangaroos led to the implementation of a "Macropod Management Plan" in 2010.

"It included the replacement of grazing habitat such as grasslands with shrubs, and the fencing of potential access areas," the company said.

The Department of Environment, Land, Water and Planning (DELWP) said it authorised the action taken by Portland Aluminium to assess the health of koalas within the plantation surrounding the facility, which is owned by the company.

"The delivery of the program was in line with the conditions of the authorisation and associated protocols and procedures to ensure koala welfare was protected," a DELWP spokesperson said.