A state superfund site in West Islip that had undergone decades of treatment for groundwater and soil contamination poses a new threat after monitoring tests revealed high levels of the carcinogen cadmium nearby in sediment at Willet’s Creek.

The state Department of Environmental Conservation put out a notice last week saying the former site of Dzus Fasteners Co. on Union Boulevard had been reclassified from a closed status to one that indicated a significant threat to public health or the environment.

The notice, which said the contamination was likely from leaching pools that had been removed as part of site remediation, said the cadmium could harm aquatic and human health.

“The cadmium levels in the wetland sediment are a significant threat to human health and the environment,” DEC said in the public notice.

DEC officials said they believe the contamination was kicked up by flooding when superstorm Sandy hit in 2012.

Subsequent, routine monitoring of the creek in 2013 and 2014 showed elevated levels of the compound and that was eventually traced back to an isolated, overgrown floodplain area near the site.

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The agency could not provide the concentration of cadmium measured. “They were elevated,” a DEC official said of the levels. “They were certainly something that got our attention.”

DEC said drinking water is not affected and that the agency is assessing how to clean up the area, which will likely include removing contaminated soils or sediment.

It’s rare for the state to reclassify sites upgrading the danger. The Dzus site was considered a class 4, which meant remedies were in place but monitoring still required.

“It’s the checks and balances of why we rank the sites class 4,” the DEC official said. “If we see something that is different, we try to find out what is making it different.”

Dzus opened on the site in 1937 and manufactured cadmium-plated fasteners for military aircraft and other uses. Leaching pools were used to dispose of hazardous waste. The DEC began investigating the site in the 1980s, finding eventually that soil and groundwater were contaminated with cadmium, chromium, cyanide and organic compounds, according to a DEC site record.

In 1990, nearly 2,000 cubic yards of soil was removed from the leach field. Nine years later, 19,000 cubic yards of sediment were removed from Willet’s Creek and Lake Capri, which is fed by the creek.

Dzus changed its name to DFCI Solutions Inc. in 2001 before it was bought in 2014 by Southco Inc., which also manufactures fasteners, hinges, locks and other items for a variety of industries in North America, Europe and Asia.

A spokeswoman for Southco said in an email the company never owned DFCI real estate or operated from West Islip. She referred calls to DFCI, who referred calls to DEC.

Willet’s Creek flows along the eastern border of nearby Beach Street Middle School and West Islip High School. Syntax, a public relations firm representing the West Islip Public Schools, said the superintendent alerted the community.

Cadmium is a naturally occurring element that does not easily corrode. It gets into the environment through mining, industrial activities, burning coal and household waste, according to the Agency for Toxic Substances and Disease Registry.

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Cadmium and cadmium compounds are carcinogenic. Breathing in high levels can cause lung damage and long-term exposure can lead to kidney disease.

The state Department of Health did not respond to a request for information. But the agency has an ongoing alert warning people about consuming eel, carp and other fish from the lake. Lake Capri is also listed as an impaired water body with the state and U.S. Environmental Protection Agency because of chlordane and cadmium pollutants.

Grace Kelly-McGovern, spokeswoman for the Suffolk County Department of Health Services, said the agency had reached out to DEC and the state health department for more information. “We will work with state agencies to ensure appropriate actions to protect public health are taken,” she said.

CORRECTION: An earlier version incorrectly stated how close the former site of the Kirdahy Elementary School, which no longer houses West Islip school district students, was to Willets Creek.