In this June 18, 2018 file photo, equipment used to test for perfluoroalkyl and polyfluoroalkyl substances, known collectively as PFAS, in drinking water is seen at Trident Laboratories in Holland, Mich.

A group of toxic “forever” chemicals that have popped up in Connecticut water supplies are potentially more dangerous than previously thought, federal authorities announced this week, prompting regulators to slash recommended levels at which the chemicals may appear in drinking water.

On Wednesday, the Environmental Protection Agency announced that new research of per- and polyfluoroalkyl substances, or PFAS, suggested that some of the thousands of chemicals included within that group can cause adverse health effects even at levels so low that they cannot be detected through water quality testing.

As a result of those findings, the agency issued temporary guidance to set acceptable limits for two common types of PFAS chemicals at near-zero levels, in addition to other updates from its last health advisory on the chemicals issued in 2016.

The Connecticut Department of Public Health followed up on the announcement on Wednesday by imposing its own non-binding limits on PFAS in drinking water, which are used by utilities, local health authorities and other state agencies to determine when action is needed to improve water quality.

The new limits set acceptable levels for certain PFAS chemicals as low as 10 parts per trillion, down from the previous “action” level of 70 parts per trillion across the family of chemicals.

“The new action levels for individual PFAS reflect the evolving scientific evidence on their toxicity and are more protective of public health than the previous Connecticut action levels,” Public Health Commissioner Manisha Juthani said in a statement announcing the change.

The Aquarion Water Company released a statement on Thursday saying that the company has already engaged in voluntary testing of PFAS in its service area, with the results of those tests published online.

“Aquarion has been proactively planning for potential infrastructure upgrades which may include new water interconnections or PFAS treatment,” a company spokesman, Peter Fazekas, said in a statement. “Designing and installing PFAS treatment facilities can be expensive. To help offset costs to customers, Aquarion is actively seeking funding through the federal Infrastructure Investment and Jobs Act.”

Daniel Meaney, a spokesman for the Connecticut Water Company, said in a statement late Thursday that the company is also conducting voluntary testing while waiting for additional guidance from regulators.

“Connecticut Water has been exploring options for PFAS treatment which can require a significant investment, as it awaits the setting of PFAS standards by EPA and DPH,” Meaney said. “Connecticut Water will continue to update customers on PFAS and our plans to remain in compliance with state and federal water quality standards for PFAS as they are developed and approved by EPA/DPH.”

The ubiquitous chemicals — used in everything from firefighting foams to food wrappers and non-stick cookware — have been linked to weakened immune systems, liver problems, low birth weights and certain cancers, according to the EPA.

PFAS chemicals take an extremely long time to break down in the environment and can build up over years in the human body, causing experts to dub them “forever” chemicals.

Officials in Connecticut first raised alarms about PFAS contamination in 2019, following a pair of accidents at Bradley International Airport in Windsor Locks that caused thousands of gallons of firefighting foam containing the toxic chemicals to flow into the Farmington River, triggering warnings against eating fish caught from the river.

The accidents prompted Gov. Ned Lamont to establish a task force that later recommended wide-scale testing for PFAS chemicals at private wells and drinking water supplies across the state.

Lawmakers also responded, enacting a ban on the use of PFAS chemicals in food packaging and most firefighting foams.

Testing early last year uncovered levels of PFAS that far exceeded the state’s action levels at more than a dozen private wells around the town of Killingworth, prompting local officials and the Department of Energy and Environmental Protection to expand testing and install new water filters on the affected wells.

Ray Frigon, the assistant director of the Remediation Division at DEEP, said on Thursday that an investigation set to begin later this month will focus on a former firefighting training facility as the “main suspect area” for the contamination in Killingworth.

In addition, he said DEEP has tested roughly 150 wells around the state and found high levels of PFAS in 35, mostly in the Killingworth area.

“We’ve learned so far that PFAS is so ubiquitous, it is in so many different products,” Frigon said. “The chances of finding PFAS are very high, we’re finding it in remote areas of the state where there are no known releases.”

In addition to its health advisory, the EPA on Wednesday announced that it would make $1 billion in funding available through the bipartisan infrastructure law to help state’s address PFAS contamination.

Frigon said Connecticut will “most definitely” apply for some of that funding, as DEEP and DPH work to coordinate their efforts and expand testing in areas where possible sources of PFAS contamination have been identified.