Cambridge’s Walter J. Sullivan Water Purification Facility. (Photo: Marc Levy)

Levels of a worrisome group of chemicals that have been linked to health problems have been rising in Cambridge drinking water despite new filters in the city’s water treatment plant that were installed to lower the concentration. The proportion of the chemicals, called per- and polyfluoroalkyl substances and abbreviated as PFAS, increased to the point where in January the level of one of them exceeded a proposed federal limit.

None of the PFAS levels in Cambridge water have been higher than current state and Environmental Protection Agency limits, though.

Mark Gallagher, acting managing director of the city water department, said the increase in PFAS levels was expected because the new carbon in the water treatment plant filters had a finite ability to remove contaminants. As the filter media reached one year of use last fall and PFAS concentrations started rising, the department began planning to replace the carbon, Gallagher said.

The city finished installing new carbon in two of the six filters in February, Gallagher said; the sample that produced the level exceeding the proposed EPA standard was taken in January, he said. Work on two more filters will be finished by the end of next week and work on the last two will start a month after that, Gallagher said.

When all six filter replacements are complete,  “we fully anticipate our PFAS results return to a non-detect level,” he said.

Margin for error

Gallagher also pointed out that lab results for PFAS have a potential 30 percent error; they are measured in parts per trillion, an infinitesimal amount.The January result that exceeded the proposed federal limit was for a subgroup of the chemicals called PFOA, or perfluorooctanoic acid, the most common type. The lab found 4.95 parts per trillion of them compared with the proposed limit of 4 parts per trillion. With a 30 percent error the true result could have been below the limit.

PFAS include more than 1,000 individual chemicals that resist water, grease, stains and heat. They have been used widely since the 1950s in products such as food packaging, non-stick cookware and firefighting foam. Known as “forever chemicals,” they are extremely stable and ubiquitous in the environment, found in soil, water bodies, fish and other animals, including people.  In humans, depending on exposure, the chemicals have been linked to health effects including certain cancers, immune system dysfunction, high cholesterol, developmental problems in children and reproductive difficulties such as reduced fertility.

Cambridge decided in 2022 to replace the carbon in the water treatment filters because of rising PFAS levels; when supply chain problems delayed the work, the city switched to Massachusetts Water Resources Authority water from the Quabbin Reservoir, which had non-detectable levels. The city started using MWRA water in late August 2022 and resumed using its own supply in November 2022 after installing new carbon in the two of the filters, completing the remaining four later.

Gallagher said it takes five tractor-trailer loads of carbon and about three weeks of work to replenish one filter.

Raising concerns

Cambridge resident Joseph Poirier brought attention Wednesday to the rising concentrations in an email to city councillors, which Cambridge Day has seen. Poirier pointed out that if proposed federal limits are adopted, Cambridge won’t comply with the the standard, assuming levels remain where they are. Poirier advocated a study of switching to the MWRA system, and to make the switch if its water is safer.

The regulatory picture for the chemicals is contradictory and uncertain. In 2016, the EPA recommended a drinking water limit of 70 parts per trillion for the sum of two types of the chemicals, and the state Department of Environmental Protection set a more stringent limit: an average of 20 parts per trillion for the sum of six types, including the two cited by the other agency. EPA went further in July 2022, saying it was considering limits of hundredths and thousands of one part per billion for the two chemical types, or essentially zero.

Those limits were just suggestions. On March 14 the agency formally proposed much higher limits for the two types of PFAS chemicals it had formerly singled out: 4 parts per trillion. Four other types would be subject to a “hazard index,” a formula that compares the level in a water system’s drinking water to the maximum amount the agency has determined won’t endanger health. Because of the formula, it wouldn’t be easy to figure out  whether the state maximum is still higher than the proposed limit in all cases.