Natural bacteria degrading pollutants in Sydney Harbour

Why can't you eat fish caught west of the Harbour Bridge?

Underneath its world-renowned beauty, Sydney Harbour remains affected by dioxins. These pollutants spread from a former chemical manufacturing plant at Homebush Bay. While the Harbour is cleaner than it once was, repeatedly eating contaminated fish carries several health risks, including increasing your risk of cancer.

But what if we could clean Homebush Bay once and for all?

Bacteria breaking down pollutants

UNSW researchers have shown that bacteria already living in the bay have begun to break down pollutants. They propose that boosting this bacterial population will decrease the time taken to degrade these pollutants.

“If you can elevate bacterial concentrations a thousand‑fold, you can degrade contaminants a thousand‑fold faster,” says UNSW’s Civil and Environmental Engineering Professor Michael Manefield. “So instead of taking 50 to 100 years to naturally attenuate, it could be five, 10 years.”

Using bacteria this way is a form of bioremediation – using microorganisms to clean polluted environments. It is a cheaper and more sustainable alternative to methods like building barrier walls or capping or immobilising soil.

“Heavy engineering approaches like digging and dumping, pumping and treating are prohibitively expensive, energy‑intensive and generate a lot of greenhouse gas emissions,” says Prof. Manefield.

The NSW government previously used heavy engineering at Homebush Bay by digging out the most contaminated sediment and destroying pollutants at a significant cost. While this substantially reduced pollution, a significant amount remains. Officials hoped these pollutants would naturally degrade over time, keeping safety measures like the fishing ban in place to manage the risk.

Homebush Bay’s Vietnam War legacy

This enduring contamination drew Prof. Manefield to Homebush Bay. He has spent much of his career growing and deploying bacteria to clean polluted sites across Australia, such as the former munitions site at Melbourne’s Deer Park.

However, a trip to the War Remnants Museum in Vietnam spurred his work at Homebush Bay.

“I saw these harrowing photos of deformed children from the application of Agent Orange during the Vietnam War,” he says. “That stuff [Agent Orange] was being synthesised on the Rhodes Peninsula in Sydney. That was part of Australia’s contribution to the war effort.”

The dioxins produced as a byproduct in Agent Orange, which cause severe health consequences in Vietnam, are the same ones contaminating Homebush Bay today.

“I work with bacteria that break down these kinds of chemicals, so I thought maybe I should be looking into that,” explains Prof. Manefield.

Developing the technology

Professor Manefield and his co-researchers compared bay sediment to measurements taken a decade earlier. They found a specific bacterium, naturally occurring in the bay, was breaking down pollutants.

In the lab, the team successfully grew the bacteria, suggesting they could produce it at the necessary scale.

Distributing the bacteria through the sediment presents a major engineering challenge.

"Harbour sediments are really tough to biologically remediate...the water above the sediments is moving, but the water in the sediments is static, so it doesn’t spread the bacteria around,” says Prof. Manefield. “It’s a distribution issue.”

To solve this, the team developed a payload system that directly injects bacteria from cartridges  into the sediment at high spatial resolution negating the need for natural distribution.

“It’s a question now of being able to scale that up, using heavy machinery and boom arms on barges,” says Prof. Manefield. This injection approach treats contaminated sediment without installing permanent infrastructure, reducing costs and preserving the bay’s appearance.

Next steps

The team is pursuing funding for large-scale trials. This technology has uses beyond industrial harbours; it can work where there’s no natural way to distribute bacteria.

"The idea is to generate a technology that can be used everywhere," says Prof. Manefield. This includes saturated sediments in rivers and lakes, as well as unsaturated soil, which is notoriously difficult to treat without digging it up.

Cleaning land sustainably

As cities grow, developing contaminated land is an ongoing concern. Recent clean-up efforts at Barangaroo, the Parramatta Light Rail, and Melbourne’s West Gate Tunnel ran significantly over budget. Australia has more than 260,000 contaminated sites, including former gasworks, refineries, and petrol stations.

“The remediation technologies we're using at the moment are not economically sustainable, which means a lot of sites that get contaminated, don't get cleaned up,” says Prof. Manefield. He suggests a proactive approach using bioremediation rather than waiting for expensive development to prompt action.

"You're not kicking the can down the road and making contaminated land a problem for the next generation."