A set of "dangerous and insidious" chemicals detected at a river near a World Heritage site have been traced back to a former quarry used by manufacturing giant 3M.
PFAS soil, sediment, groundwater and surface water have been found across a 100-hectare area of the inactive Brogans Creek lime quarry northwest of the Blue Mountains, the NSW Environment Protection Authority says.
The environment authority has for the first time issued a notice and taken regulatory action against 3M and its local Australian arm.
The quarry, in the state's central west, was historically used by 3M to test PFAS-containing firefighting foam.
While "the scale of the onsite contamination is significant", there is limited human exposure because of the remoteness of the site, the environment regulator said.
However, it found some of the chemicals eight kilometres downstream in the Capertee River within a national park.
The levels found were above the national drinking guidelines.
Ian Wright, an environmental science professor at Western Sydney University, said more data needs to be gathered about the "dangerous and insidious" chemicals.
"The Capertee River is just upstream of the Blue Mountains World Heritage area so it has extremely high biodiversity values," he told AAP.
"Because these chemicals build and build ... it's a silent burden that humans and animals are carrying around ... that could have very poor health outcomes."
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 have been dubbed "forever chemicals" because they break down extremely slowly.
Emerging evidence has linked some PFAS to cancer, leading to tighter regulation of the substances, particularly in drinking water.
Even though the environment authority commended 3M for its co-operation, it said this is only the first step in what is likely a complex and lengthy remediation process to follow.
Dr Wright warned this could be the beginning of a protracted legal battle to ascertain whether 3M or the local council ends up cleaning up the chemicals.
"It's probably contaminated forever ... once the contamination is there, it's there for multiple lifetimes," he said.
High-level contamination was detected in the drinking water catchment serving 30,000 people in the Blue Mountains in mid-2024.
An eight-month WaterNSW investigation released earlier in May found contamination of two dams used for Blue Mountains drinking water may have occurred after separate motor vehicle accident sites on the Great Western Highway in 1992 and 2002 near the Medlow Bath township.
The town's fire station was also a possible source of contamination.
Test samples at all three sites revealed the chemical compound signature consistent with the historical use of PFAS-containing fire-fighting foam, banned nationwide in 2007.
Under the authority's clean-up notice, 3M Australia has 60 days to submit a detailed plan to manage PFAS pollution.
"This is a significant moment for the EPA and one that represents an important milestone in our efforts to address legacy environmental harm," the authority's operations director David Gathercole said.
"Though this is only the first step ... 3M has so far been co-operative voluntarily offering to conduct investigation to better understand the extent and legacy of PFAS contamination."
The company has been contacted for comment.
