As federal regulators addressed concerns Monday night about the health effects of drinking water contaminated by chemicals used at naval bases in Bucks and Montgomery Counties, one answer remained elusive: What is the impact of drinking the contaminated water for decades before the contaminants were discovered?

"The short answer is, we really don't know and we really can't answer that," Karl Markiewicz, a toxicologist for the Agency for Toxic Substances and Disease Registry, told about 200 Horsham residents at Hatboro-Horsham High School.

Since 2014, 16 public wells and dozens of private wells have been shut off in Horsham, Warrington, and Warminster Townships because they are tainted with PFOA and PFOS, compounds in firefighting foams used at former naval bases in Willow Grove and Warminster.

PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate) have been linked to high cholesterol, some cancers, and other health issues.

And as the military tests more than 600 bases across the country for similar water contamination, officials have said that actions taken here could help shape the response nationwide.

U.S. Reps. Brendan Boyle, Michael Fitzpatrick, and Patrick Meehan also spoke to the crowd gathered Monday in the high school auditorium.

Boyle, a Democrat, has joined Republicans Fitzpatrick and Meehan to push for the Navy to fund blood tests for residents affected by the contaminated water. The Navy has declined, and has told the lawmakers that federal health agencies do not recommend blood testing.

Markiewicz said a study was done on levels of the contaminants in residents' blood in New Hampshire, where there was similar contamination.

That study concluded that levels were not unusual compared with the level of PFOS and PFOA in most Americans' blood, Markiewicz said. He said he believed a study here would yield the same results.

The New Hampshire study showed blood levels "certainly way lower than the high or very high exposure," he said. "I think it's important to keep that in mind."

The congressmen, however, continued to tell residents they will push for blood testing and health studies.

"We will continue that fight when we go back to Washington," Meehan said.

The Environmental Protection Agency in May lowered the level of contaminants considered safe to drink, leading to more well closures.

Federal officials told residents Monday that their tap water is now safe.

But in Horsham, the township council has voted to purchase water from neighboring water suppliers, expressing doubt about the quality of their water.

A report analyzing cancer data in Warrington, Warminster, and Horsham released this month found that instances of some cancers, such as bladder cancer, increased over the last few decades, but did not qualify as a cancer cluster. The data were "inconclusive," said Sharon Watkins of the Pennsylvania Department of Health.

Watkins said that officials will continue to track cancer data, but that it is challenging to study the relatively small sample group, based only on the zip code where people live at the time of their diagnosis.

"That makes it a little bit more difficult to say 'aha' in this kind of analysis," Watkins said. "We are certainly looking at this as a first cut."

Keith and Dina Clerkin of Horsham attended the meeting to learn more about the health effects of the chemicals, and in hopes that they would hear whether blood tests will be made available. Dina Clerkin said she struggles with arthritis and wonders if it could be connected to the tainted water.

"I'm trying to get more information about where do we go from here," she said.

As the meeting ended, one resident stood and shouted that she wanted additional clarification to her question, because residents had been asked to submit questions in advance. Others shook their heads. The panelists encouraged residents to speak with them individually.

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