We proved these ‘forever chemicals’ can last longer than three decades

The fresh air, picturesque vistas and pristine bush of the Blue Mountains west of Sydney draw millions of visitors a year.

Unfortunately, the Blue Mountains are also the site of a controversial investigation into water contamination with “forever chemicals”, also called PFAS.

Our recent study investigated long-term PFAS contamination from two incidents, both involving petrol tanker crashes and fires. Both accidents occurred in drinking water catchments, and our study found contamination was present but undetected for 24 and 33 years, respectively. We have searched the international literature and could not find similar examples.

PFAS (Perfluoroalkyl and polyfluoroalkyl substances) are a broad category of thousands of synthetic chemicals used in numerous consumer and industry products. Exposure to PFAS is associated with a greater risk of several illnesses.

Our research shows how vulnerable drinking water supplies are to long-term PFAS contamination. It also shows how contamination can remain hidden due to an absence of PFAS monitoring.

Two historical accidents

The 1992 petrol tanker accident in the Blue Mountains at Medlow Bath caused PFAS contamination of the local drinking water supply. And 32 years later it forced the closure of two storage reservoirs.

Despite limited data, we identified the source of contamination as a type of foaming material used globally by firefighters to help extinguish burning fuel fires. This foaming substance was mixed with water using perfluorooctane sulfonate, a type of PFAS.

Firefighters used this substance to form a foam “blanket” and coat burning materials and extinguish liquid fires. The PFAS foams were used for decades before their harmful human health and environmental impacts were understood.

Nine years after the first petrol tanker accident, another fuel tanker crash and fire linked to PFAS contamination occurred in 2000, near Ourimbah on the NSW Central Coast. The fuel tanker was carrying 40,000 litres of fuel, and the crash and fire were triggered by a collision with a car. This resulted in the tragic death of two people.

Similar to the Medlow Bath accident, news footage showed water and foam were used to control the blaze. It also showed a foamy runoff draining from the accident.

Why are PFAS a problem?

PFAS, often called “forever chemicals”, are a broad category of thousands of synthetic chemicals. They are used in numerous products, such as non-stick cookware, stain-resistant fabrics, takeaway food packaging and even cosmetics.

PFAS molecules don’t easily break down, and readily accumulate in tissue of wildlife across the globe. Exposure to small amounts of PFAS sees the chemicals build up in the vital organs of animals and people. Analysis of human autopsy tissue revealed accumulation of PFAS in the brain, lungs, liver, kidney and bones.

In 2025, an Australian Bureau of Statistics report revealed nearly all Australians have PFAS chemicals accumulating in our bodies.

Should we be worried?

Exposure to PFAS is associated with a greater risk of several illnesses. These include decreased fertility, higher blood pressure, increased risk of cancer (particularly prostate, kidney and testicular cancers), liver disease, higher cholesterol and obesity.

One of the humans are likely to consume PFAS is through eating foods containing PFAS and in drinking water.

The Upper Blue Mountains water supply serves about 40,000 people, and operated by Sydney Water Corporation. It reported that one of the most hazardous forms of PFAS, PFOS, reached 16.4 nanograms per litre in the local drinking water on June 25 2024. This is double the safe amount, according to the recently revised Australian drinking water guidelines.

Discovery of PFAS triggered the closure of two drinking water reservoirs downstream of the Medlow Bath petrol tanker crash and fire. Although a lack of testing data creates uncertainty, it is likely PFAS contamination was undetected in the Blue Mountains drinking water supply for more than 30 years.