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In an October study, researchers at the Harvard School of Engineering and Applied Sciences discovered that fish can accumulate elevated levels of synthetic chemicals up to five miles away from the original source of pollution.

These chemicals are called per- and poly-fluoroalkyl substances — or PFAS — and they are linked to adverse health effects including an increased risk of various cancers.

The study — published in the journal Environmental Science and Technology — found that PFAS can travel far from the source of emission as long as the contaminated site is connected to surface water bodies.

The SEAS researchers took various field samples downstream from a military base in Cape Cod that had historically used aqueous film-forming foam — a fire suppressant.

Heidi M. Pickard, the study’s lead author, said her research team had previously analyzed water sites to find downstream contamination from the foam, but they had not studied the various fish and shellfish species.

Pickard’s study revealed that fish and shellfish far from a source of contamination accumulate high levels of these chemicals as well.

“They’re persistent chemicals. They can move from groundwater to surface water to groundwater to surface water, all the way out to the estuary into the open ocean,” Pickard said.

The paper reported PFAS contamination from the upstream military site remained detectable at distances up to five miles from the source.

Mary M. Johnson, a scientist at the Harvard School of Public Health who was not involved in the study, said she was shocked by the findings.

“I was a little bit horrified by the study results,” said Johnson, who specializes in environmental health. “I was surprised to see that five miles away they could detect increased concentrations from the source.”

The study also revealed gaps in existing abilities to measure PFAS levels.

“If you’re only looking within a small vicinity close to that contaminated site, then you’re likely underestimating the potential exposure for people further downstream away from these contaminated sites,” Pickard said.

Current analytical methods only measure a subset of PFAS, but Pickard’s work revealed that precursor PFAS are highly vulnerable to accumulation. “You’re really underestimating potential exposure and the potential risk to fish consumers,” she said.

The researchers hoped their findings would guide future environmental monitoring.

“This contamination isn’t going anywhere, and it’s going to continue being a source of contamination to people’s drinking water and to these fish downstream,” Pickard said. “Unless you deal with that contamination at the source — unless you deal with what’s in that soil — it’s going to continue leaching out into the groundwater over time for many, many decades to come.”