Forever chemicals in US tap water linked to high incidences of certain cancers, researchers warn

Communities across the US that are regularly exposed to drinking water contaminated with manufactured per- and polyfluoroalkyl substances (PFAS) known as “forever chemicals” experience up to a 33% higher incidence of certain cancers, warn researchers at the Keck School of Medicine of USC.

Their new study is the first to examine the link between cancer and PFAS-contaminated drinking water in the US. The pervasive chemicals, which are used in consumer products such as furniture and food packaging, have been found in around 45% of drinking water supplies across the country.

Past research has linked the chemicals, which are slow to break down and accumulate in the body over time, to a range of health problems, including kidney, breast and testicular cancers. PFAS has even been found in human breast milk, triggering immune-related issues in infants.

In the US, PFAS in drinking water are estimated to contribute to more than 6,800 cancer cases each year, based on the most recent data from the Environmental Protection Agency (EPA).

“When people hear that PFAS is associated with cancer, it’s hard to know how it’s relevant. By calculating the number of attributable cancer cases, we’re able to estimate how many people may be affected,” says Shiwen (Sherlock) Li, Ph.D., a postdoctoral researcher in the Department of Population and Public Health Sciences at the Keck School of Medicine and first author of the study. 

Mapping spread of forever chemicals

To paint a more comprehensive picture of PFAS and cancer risk, Keck School of Medicine researchers conducted an ecological study, which uses large population-level datasets to identify patterns of exposure and associated risk.

The researchers compared two exhaustive datasets — one covering all reported cancer cases and the other including all data on PFAS in drinking water across the country.

The researchers then compared cancer incidence in each county to PFAS contamination in the drinking water, using the EPA’s recommended cutoffs for each type of PFAS.

At the individual level, control factors included age and sex; at the county level, the researchers ruled out changes in cancer incidence due to socioeconomic status, smoking rates, obesity prevalence, urbanicity (how urban or rural an area is) and the presence of other pollutants.

The team discovered that counties across the US with PFAS-contaminated drinking water had higher incidences of certain types of cancer, which differed by sex, between 2016 and 2021.

Males in counties with contaminated drinking water had a higher incidence of leukemia, as well as cancers of the urinary system, brain and soft tissues, compared to males living in areas with uncontaminated water.

In the US, PFAS in drinking water are estimated to contribute to more than 6,800 cancer cases each year.Females had a higher incidence of cancers in the thyroid, mouth and throat, and soft tissues.

Counties where drinking water surpassed recommended maximum levels of PFAS had a higher incidence of digestive, endocrine, respiratory and mouth and throat cancers. Increases in incidence of mouth and throat cancers linked to perfluorobutanesulfonic acid ranged from slightly elevated at 2% to substantially elevated at 33%.

Regulatory efforts fall short

These population-level findings reveal associations between PFAS and rare cancers that might otherwise go unnoticed.

On the regulation side, the results add to mounting evidence that PFAS levels should be limited. However, the study authors warn these proposed changes may not go far enough.

Li says that starting in 2029, the EPA will police levels of six types of PFAS in drinking water, but stricter limits may ultimately be needed to protect public health.

“Certain PFAS that were less studied need to be monitored more, and regulators need to think about other PFAS that may not be strictly regulated yet,” he stresses.

In future research, individual-level studies are needed to determine whether the link is causal and to explore what biological mechanisms are involved.

The research, funded by the National Institutes of Health, was published in the Journal of Exposure Science and Environmental Epidemiology.

In other PFAS research, Swedish scientists found the chemicals may impact human health as early as the fetal stage of development. Another US study flagged their alarming presence in freshwater fish, while an Environmental Working Group report warned of their likelihood of turning up in pet food.