The U.S. Environmental Protection Agency (EPA) has decided not to impose limits on perchlorate in drinking water, upholding a decision from the Trump administration.

Perchlorate, a chemical component found in rocket fuel and explosives such as fireworks, is considered a contaminant that has been linked to brain damage in newborns and infants. The decision could affect as many as 16 million Americans.

“While EPA is not pursuing a drinking water regulation at this time, the agency will continue to consider new information on the health effects and occurrence of perchlorate,” the EPA said in a statement.

In 2020, the Trump administration opted not to regulate perchlorate, saying that the chemical didn’t meet the criteria for regulation because it didn’t appear in drinking water “with a frequency and at levels of public health concern.” After the decision, public health experts criticized EPA and said the agency disregarded science.

After President Joe Biden took office, EPA launched a review of the previous decision and it said that it endorsed the Trump administration decision, noting that it was “supported by the best available peer-reviewed science.”

At the same time, EPA said it would provide $11.7 billion in the Bipartisan Infrastructure Law to address drinking water issues by setting up new monitoring tools and cleaning up contaminated sites. The agency also said it will create an online toolkit with technical information for drinking water systems and communities that have concerns about perchlorate contamination, which will be available sometime in 2022.

The EPA decision doesn’t affect state standards that regulate the chemical. California and Massachusetts have set limits for perchlorate in drinking water.

Perchlorate can occur naturally, particularly in arid regions, such as the southwestern United States, though high concentrations have been found in at least 26 states. High levels are often detected near military installations where the chemical has been used in rocket fuel to make propellants more reliable.

The discussion around perchlorate dates back to the early 2000s, when the Bush administration decided not to regulate the chemical in drinking water. The Obama administration reversed the decision, saying that perchlorate posed a serious health risk for millions of Americans and recommending that states create a limit of 15 micrograms per liter. The Department of Defense and military contractors, such as Lockheed Martin and Northrop Grumman, fought against the limits.

The Trump administration reversed the Obama administration’s decision and said it was “not in the public interest” to regulate the chemical. Environmental groups sued EPA over the decision, but paused the lawsuit after Biden was inaugurated in 2021.

The litigation will now resume, with the goal of compelling EPA to impose standards for perchlorate.