More types of chemicals that do not naturally break down have been detected in tap water, backing up calls for nationwide testing.

Among more than 20 chemicals previously undetected in Australian tap water is one occasionally found in bottled water, and another previously undetected contamination from firefighting foams.

The increased detections in samples from Sydney drinking water coincides with increased monitoring and concerns over the level of the contaminants considered safe, with some exceeding international guidelines.

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“Sydney’s water meets current Australian standards, but when considering health benchmarks used in other countries, some samples were near or above safety limits,” University of NSW chemistry professor William Donald said.

He was the lead author of a study in environmental chemistry journal Chemosphere which reported the analysis of 32 tap water and 10 bottled water samples from Sydney catchment areas in early 2024.

PFAS, or per- and polyfluoroalkyl substances, are a group of 15,000 highly toxic, synthetic chemicals used for their resistance to heat, stains and grease.

They are sometimes called “forever chemicals” because they break down extremely slowly, including in humans.

The researchers detected 31 chemicals, including 21 not previously recorded, as scientists grapple with removing the chemicals from the environment.

The task is made more difficult by tiny tweaks in chemical structures creating new compounds, requiring their own assessments for toxicity, environmental persistence and potential health impacts.

“We are stuck in a whack-a-mole situation with PFAS,” Donald said.

Regulating the compounds as a class of chemicals rather than individually could ease the burden.

A mobile filtration system was installed following the detection of PFAS chemicals at elevated levels in untreated water flowing into the Cascade water filtration plant in the NSW Blue Mountains in September.

Researchers are also working on materials designed to absorb and break down the chemicals in water.

The National Health and Medical Research Council updated its guidelines in June, but resisted implementing a draft guideline on perfluorooctane sulfonic acid (PFOS), allowing double the concentration first floated.

If the 4ng/L guideline used by the United States Environmental Protection Agency had been adopted, the levels detected from samples at North Richmond in Sydney’s northwest would have exceeded them.

PFOS - a known carcinogen used in firefighting foam - was detected at 6ng/L in some of those samples, 2ng/L below the Australian guidelines.

Dr Lisa Hua, who along with Donald, detected PFAS in the “tar balls” which closed Sydney beaches in October, said the low concentrations provided some reassurance.

But new technologies to remove the chemicals from the environment and prevent their release should be explored, and wider testing could provide more insight into the level of contamination across Australia.

“Expanding the current monitoring of PFAS could be beneficial to gain a greater understanding of seasonal variations of PFAS in drinking water supply,” Hua said.

Import, export, manufacture and use of some PFAS chemicals was banned nationwide in July.

Europe is mulling a union-wide PFAS monitoring framework to collect data and map pollution.