The number of US service members who have been exposed to toxic “forever chemicals” is much higher than the military has claimed, a new independent analysis of Department of Defense data has found.

A Pentagon report that aims to assess the scope of PFAS chemical exposure on its bases, as well as health threats posed to service members, estimated about 175,000 troops across 24 facilities had drunk contaminated water.

But an analysis of the military’s report by the Environmental Working Group (EWG), a non-profit that tracks PFAS pollution, found the numbers are probably much higher and could top more than 640,000 people across 116 bases, and potentially even millions of people when past service members are factored in.

Moreover, the report seemed to omit health issues linked to PFAS exposure, such as kidney disease, testicular cancer and fetal effects. The overall report is “frustrating”, said Scott Faber, senior vice-president of government affairs with EWG.

“The Department of Defense is trying to downplay these risks rather than aggressively seeking to notify service members and clean up its legacy pollution,” he said. “It has long history of looking the other way when it comes to PFAS pollution.”

The DoD did not immediately respond to a request for comment.

PFAS are a class of about 12,000 chemicals often used to make products resist water, stain and heat. They are called forever chemicals because they do not naturally break down and persist in the environment. The chemicals are linked to cancer, liver disease, high cholesterol, thyroid disorders, birth defects and autoimmune dysfunction.

PFAS are thought to be contaminating drinking water for more than 200 million people nationally, and contamination has been found in and around hundreds of DoD bases at high levels because the chemicals are the main ingredient in firefighting foam the military uses.

Congress mandated the DoD report in the 2019 National Defense Authorization Act, but the military has not published it on the department’s PFAS website, so it is unavailable to the public or service members except upon request.

“That’s the part that ought to bother every American,” Faber said. “It’s not just that they purposefully underestimated how many service members were exposed … it’s that they didn’t tell anyone.”

The DoD’s analysis, dated April 2022, seemed designed to reduce the exposure estimates in several key ways, EWG noted.

It only included bases where levels for two types of PFAS – PFOS and PFOA – exceeded the Environmental Protection Agency’s previous health advisory limit of 70 parts per trillion (ppt). But the EPA lowered that level in June to less than 1 ppt for each compound.

Though the report came out about two months before the change, the military often lobbies the EPA on environmental rules, the pending change was publicly known, and the military likely rushed to get its report out ahead of the EPA’s formal announcement, Faber said.

“This is clearly what it appears to be,” he said.

The numbers also did not include four large bases – Fort Bragg, Yakima Training Center, Fort Leavenworth and Picatinny Arsenal – where levels ranged from 98 ppt to 647 ppt.

The levels peaked at over 21,000 ppt at Horsham air national guard base in Willow Grove, Pennsylvania.

The report also only considered military members who were on bases at the time of the analysis, meaning it is a “snapshot in time”. The military began using firefighting foam with PFAS over 50 years ago.

“The real question is how many millions of service members drank the contaminated water over the last half century?” Faber asked.

The numbers would probably be higher if the military also included other kinds of PFAS. PFOA and PFOS are two of the most common, but thousands more are in commercial use, and the EPA also has health advisory limits for two other compounds.

Though Congress required the DoD to include an assessment of health risks to troops, the military excluded risks for fetal and maternal health because it “focused on military members and veterans”, the department wrote. EWG noted that about 13,000 service members give birth every year, and many live on DoD facilities. The military also made no mention of increased testicular and kidney cancer risks.

“It’s shocking and there was no explanation,” Faber said.

It is unclear what’s next for the report. Congress has ordered the DoD to phase out firefighting foam that uses PFAS by October 2023, and develop a cleanup plan. The military already missed a deadline to submit a cleanup plan to Congress, but Faber noted it has new political leadership in place, and the Biden administration has been more serious about addressing PFAS contamination than Trump.

“The next few years will be critical to resetting when it comes to the DoD addressing toxic chemicals, like PFAS,” Faber said.