Potentially toxic chemicals could have been discharging into the Kalamazoo River for some time, according to new testing carried out by the state of Michigan.

The Kalamazoo Gazette says that the Department of Environmental Quality requested earlier this year that municipalities test their wastewater treatment plants for possible per and poly-fleuoroalkyl substance contamination; after the City of Kalamazoo tested theirs, they determined that upwards of four times the state standard for certain types of PFAS were being discharged from the wastewater system into the Kalamazoo River. The City believes that 20 industrial sites are responsible for dumping the contaminants into the system.

However, the DEQ says that there isn’t evidence this PFAS contamination could be a threat to human health.

This report comes just days after the DEQ announced that four residential drinking water wells in the Richland area had high levels of PFAS, prompting the agency to provide bottled water to three of those houses; the fourth doesn’t use the well for drinking. It’s believed the former Production Plastics facility near those homes is the source of that contamination.

PFAS are chemicals used in many industrial applications that can have negative effects on human health including kidney damage and thyroid problems; the EPA says they can also harm the fetuses of pregnant women.