Over the past few months, several communities in upstate New York and New England have detected PFOA — perfluorooctanoic acid, or C8, a chemical linked to a range of health issues from cancer to thyroid disease — in their drinking water.

PFOA is a fluorinated compound that is absorbed into our bodies through inhalation or ingestion. The chemical can then accumulate in our blood serum, kidneys, and liver.

The stain-resistant and water-repellant properties of PFOA make it effective in products that act as coatings. Common consumer products with PFOA include Scotchgard, Gore-Tex, and Teflon.

The qualities that make PFOA effective in consumer products also lead to its persistence in the environment. The chemical has been detected in the serum of the general U.S. population and throughout the home and workplace.

A growing number of communities near industries or military bases that used PFOA have confirmed that their drinking water has been contaminated. What does the science say about the potential health effects of PFOA exposure?

The case against DuPont

PFOA has been produced in the U.S. since 1947. However, very little was known about the human health risks of the chemical until 2001. The Environmental Protection Agency (EPA) learned that DuPont had been hiding information about the environmental presence of PFOA near the Washington Works plant in Parkersburg, West Virginia. That began what would turn out to be a decade of PFOA-related research in this community.

PFOA was used by DuPont to manufacture Teflon beginning in 1951. During the process, PFOA was released into the air and discharged into the Ohio River. The chemical then entered the groundwater that supplies the local drinking water through hydrologic interaction with the contaminated Ohio River and rainfall recharge of groundwater through the contaminated soil.

Six public water districts in West Virginia and Ohio and hundreds of private wells were contaminated. Monitoring data show PFOA continued to increase even after a drastic reduction in emissions beginning in 2001. This is due to accumulation in the soil and slow transit time into the groundwater.

As part of a settlement from a large class action lawsuit against DuPont, a C8 science panel was established to determine potential health effects resulting from PFOA exposure. A one-year cross-sectional survey (2005-2006), known as the C8 Health Project, was conducted among approximately 70,000 residents with contaminated drinking water. The health survey included serum samples, medical information, and residential histories.

Measured mean PFOA public drinking water levels at the time of the survey ranged from 0.03 micrograms per liter (µg/L) in Mason, West Virginia, to 3.49 µg/L in Little Hocking, Ohio. Private drinking water was measured at levels as high as 22.1 µg/L.

Residents in this community where PFOA was being used in manufacturing had much higher serum levels than the U.S. overall. The median measured serum PFOA level was 28.2 µg/L with a range of 0.2 to 22,412 µg/L. For comparison, PFOA levels in the serum of the general U.S. population was 3.92 µg/L in 2005-2006.

The link between PFOA and health

The C8 science panel worked with a team of researchers to analyze all the health data collected from the community participants. Their goal was to determine if there is a probable link between PFOA exposure and any human disease.

Dozens of exposure and health studies were conducted. Researchers developed an environmental model to measure the geographic extent and magnitude of PFOA contamination from the DuPont facility over several decades. This model allowed researchers to investigate health impacts of past exposures.

Information on PFOA production, groundwater flow, and well-pumping rates were used to determine PFOA levels in the drinking water systems. In addition, maps of water distribution pipes identified who had been exposed.

After several years of epidemiologic analyses, the scientists issued their reports, identifying probable links to six health outcomes: pregnancy-induced hypertension; high cholesterol; ulcerative colitis, an inflammatory bowel disease; thyroid disease; testicular cancer; and kidney cancer. Medical monitoring is now underway and residents have started filing personal injury lawsuits against DuPont.

Widespread PFOA contamination

But communities in West Virginia and Ohio are not the only ones that have been affected by PFOA contamination. Last summer, research and advocacy group the Environmental Working Group reported 94 water systems in 27 states had detectable levels of PFOA in their drinking water.

In Hoosick Falls, New York, earlier this year, high PFOA levels led to community concern about drinking water safety. A federal class action lawsuit was later filed against Saint-Gobain Performance Plastics and Honeywell International for related PFOA contamination at their manufacturing site.

Nearby towns of Petersburgh, New York, and North Bennington, Vermont, have also detected PFOA in their drinking water. Meanwhile, drinking water contamination in Decatur, Alabama, and Cottage Grove, Minnesota, has been blamed on 3M, the primary manufacturer of PFOA.

But PFOA contamination is not just affecting communities near chemical plants. PFOA is also a component in firefighting materials used in military exercises.

Communities in Buck and Montgomery counties in Pennsylvania and Kent and New Castle counties in Delaware have detected PFOA in their drinking water, likely resulting from military activities. The Department of Defense plans to investigate 664 military sites to assess PFOA contamination from firefighting foam.

Ongoing research

The response from local officials about the safety of drinking water has been mixed. That is most likely because the EPA does not regulate PFOA levels under the Safe Drinking Water Act.

EPA’s recommended health advisory level from 2009 for drinking water is 0.4 µg/L (400 parts per trillion). There has been concern that this level is not protective enough.

In the aftermath of Hoosick Falls, the EPA in January recommended that the community not drink water with PFOA in excess of 0.1 µg/L.

In the years since the original C8 studies, more health concerns related to PFOA have emerged. Recent epidemiologic studies showed low-level exposures have been also associated with decreased antibody levels among adults living near the DuPont Washington Works facility. This has been observed among children living in a fishing community as well.

The EPA, which issued a health effects document on PFOA in 2014, is currently reviewing the existing body of PFOA data in response to the recent drinking water contamination in Hoosick Falls. Additional health studies are needed, especially in communities with known drinking water contamination. It is important to confirm results from prior studies and consider other health outcomes.

While there is some uncertainty regarding what levels are considered safe, it is certain that more communities living near military bases and former PFOA industries will be affected. Although PFOA was phased out in 2015, the contamination will persist for years to come.

Veronica Vieira is an associate professor of public health at the University of California, Irvine. This post originally appeared at The Conversation.