The EPA says it is reviewing a chemical that the agency says could be harmful to humans.
More:The agency said in a statement Monday that it would conduct a thorough review to determine whether the chemical poses a health risk.
A toxicology study conducted by the Centers for Disease Control and Prevention (CDC) is scheduled to begin next month and will be completed by late April, the agency said.
The CDC also said it was preparing an analysis of the chemical that is likely to be submitted to the Environmental Protection Agency.
The agency did not say how much of the substance could be linked to the outbreak.
This is the third time the agency has been under fire over the use of a chemical in its wastewater treatment system that has caused widespread illness.
In 2015, the EPA and the U.S. Environmental Protection Administration (EPA) said the chemical, known as thiophos, was safe for human consumption.
EPA administrator Scott Pruitt said at the time that it posed no health risk to humans and should not be used in wastewater treatment plants.
Pruitt also said the agency is reviewing the substance’s use in the agency’s wastewater treatment plant at the Ohio River.