FAIRFIELD — Toxins known as PCBs (polychlorinated biphenyls) have been found in some samples of sediment dredged from the Mill River as part of the latest cleanup of the former Exide Battery property on the Post Road.

The sediment is stockpiled on the Exide property and poses no danger to residents because of the site controls already in place, according to a statement from the first selectman’s office.

The discovery, however, has prompted a mandatory review of the project by the state Department of Energy and Environmental Protection and the federal Environmental Protection Agency under the Toxic Substances and Control Act.

The agencies will review the new sampling data and require additional authorizations prior to allowing the sediment to be moved from the property to a certified landfill facility.

Cleanup of the Exide factory property and the contamination it also caused in the Mill River has been going on for decades.

A first attempt at remediation of the Mill River was done in 1983 when about 4,000 yards of contaminated sediment was removed from the river. Ground contaminants were removed between 1987 and 1990.

But the current DEEP order was issued in 2008 when it was discovered that those initial efforts failed to reduce the lead levels in the river. There was a long process that involved town officials, residents, DEEP and the property owners to come to an agreement on how much of the contaminated sediment needed to be removed and the mechanics of that process.

It is believed the bulk of the lead contamination was caused by spills during the battery-manufacturing process.

When the factory was demolished, 13,000 tons of demolition debris, 10,000 tons of contaminated soil and 4,000 feet of contaminated pipes were removed from the Post Road property.

The sediment subsequently dredged from the river and de-watered, now sits in large brown sacks piled high on the site, waiting to be moved to an approved disposal site.

According to town officials, PCB testing was not previously required based on Exide’s past industrial practices and historical testing on the Mill River sediments revealed only low levels of PCBs “typical of any urban watershed.”

It will be up to the DEEP and the EPA if a responsible party for release of the PCBs into the river can be determined, and what the next course of action will be.