A study published Thursday warned water systems for numerous schools and day care centers in 18 states may have been contaminated by toxic chemicals produced at nearby chemical plants.

The Environmental Working Group conducted the study by looking at the water systems for schools across the U.S. at risk of contamination, focusing on finding per- and polyfluoroalkyl substances, known as PFAS or fluorinated “forever chemicals.”

“Suspected industrial dischargers of the toxic fluorinated chemicals known as PFAS are located less than a mile of 27 schools or child care facilities that maintain their own water systems,” Environmental Working Group policy analyst Jared Hayes and senior scientist Tasha Stoiber said in the report. “Schools or child care facilities in 18 states, including Michigan, Oregon, Pennsylvania and Wisconsin, were located within 5,000 feet of manufacturers that are known or suspected of producing or using PFAS.”

PFAS are chemicals commonly found everyday items, such as household cleaning and food storage products.