The water filter on your refrigerator door, the pitcher-style filter you keep inside the fridge and the whole-house filtration system you installed last year may function differently and have vastly different price tags, but they have one thing in common.
They may not remove all of the drinking water contaminants you’re concerned about.
A new study co-led by Nicholas School faculty member Heather Stapleton finds that – while using any filter is better than using none – many household filters are only partially effective at removing toxic perfluoroalkyl substances, commonly known as PFAS, from drinking water.
A few filters, if not properly maintained, can even make the situation worse.
“We tested 76 point-of-use filters and 13 point-of-entry or whole-house systems and found their effectiveness varied widely,” said Stapleton, Dan and Bunny Gabel Associate Professor of Environmental Health.
“All of the under-sink reverse osmosis and two-stage filters achieved near-complete removal of the PFAS chemicals we were testing for. In contrast, the effectiveness of activated-carbon filters used in many pitcher, countertop, refrigerator and faucet-mounted styles was inconsistent and unpredictable,” she said. “The whole house systems were also widely variable and in some cases actually increased PFAS levels in the water.”
“Home filters are really only a stopgap. The real goal should be control of PFAS contaminants at their source,” said Detlef Knappe, professor of civil, construction and environmental engineering at North Carolina State University, whose lab teamed with Stapleton’s to conduct the study.
Exposure to PFAS, used widely in fire-fighting foams and stain- and water-repellants, is associated with various cancers, low birth weight in babies, thyroid disease, impaired immune function and other health disorders. Mothers and young children may be most vulnerable to the chemicals, which can affect reproductive and developmental health.
Some scientists call PFAS “forever chemicals” because they persist in the environment indefinitely and accumulate in the human body. They are now nearly ubiquitous in human blood serum samples, Stapleton noted.
The researchers published their peer-reviewed findings in the journal Environmental Science & Technology Letters. It’s the first study to examine the PFAS-removal efficiencies of point-of-use filters in a residential setting.
Samples of filtered water from homes in six North Carolina counties were analyzed for a suite of PFAS contaminants, including GenX, which has been found in high levels in water in the Wilmington, N.C., area.
The analysis showed that reverse osmosis filters and two-stage filters reduced PFAS levels in water by 94% or more, although their high costs might put them out of reach for many of the households most affected by contamination. Activated-carbon filters, which are more affordable, removed 73% of contaminants on average.
The efficiency of whole-house systems using activated carbon filters was more variable. In four of the six systems tested, some contaminant levels actually increased after filtration.
Researchers saw no clear trends between removal efficiency and filter brand, age or source water matrix level. Changing out filters regularly is probably a very good idea, nonetheless, they stressed. Nick Herkert, a postdoctoral associate in Stapleton’s lab, was lead author on the study.