WASHINGTON (CBS Local) — The contamination of U.S. drinking water with man-made “forever chemicals” is far worse than previously estimated, an environmental group reported on Wednesday.

The Environmental Working Group (EWG), a consumer advocacy nonprofit, says it found per- and polyfluoroalkyl substances or PFAS in the water supply in dozens of major U.S. cities, with some of the highest levels found in Miami, Bergen County, N.J. and Philadelphia.

READ MORE: Michigan Gov. Whitmer Tests Positive For COVID-19, Reports 'Mild Symptoms'

“The results confirm that the number of Americans exposed to PFAS from contaminated tap water has been dramatically underestimated by previous studies, both from the Environmental Protection Agency and EWG’s own research,” the latest EWG report states.

PFAS are particularly resistant to breaking down in the environment. Some PFAS chemicals have been previously linked to cancers, liver damage, low birth weight and lowered fertility.

EWG said it tested 44 sites across 31 states and Washington, D.C., between May to December 2019, for traces of 30 different kinds of PFAS.

READ MORE: Trump Says Mar-a-Lago Was 'Raided' By FBI

Two metropolitan areas — Brunswick County, North Carolina, and Quad Cities, Iowa — have PFAS levels in water supplies above the 70 parts per trillion, or ppt, threshold the U.S. Environmental Protection Agency recommends.

EWG, however, says some studies show PFAS levels of just one part per trillion are recommended as safe. Only three cities — Seattle, Tuscaloosa, Alabama and Meridian, Mississippi — have levels below 1 ppt.

First manufactured by 3M Co. in the 1950s, PFAS have been used by industry for decades in products such as Scotchgard and Teflon because of their ability to repel water and oil.

MORE NEWS: Lighthouse Partners With Gleaners To Expand Food Relief

“It’s nearly impossible to avoid contaminated drinking water from these chemicals,” David Andrews, a senior scientist at EWG and co-author of the report, told Reuters.