There are more than 4,700 types of chemicals in the world known as PFAS. Based solely on their tongue-twister of a name — the full spelling is "per- and polyfluoroalkyl substances" — you might think that they are rare. Yet PFAS can be found absolutely everywhere: Your non-stick cookware, your fast food wrappers, your paper packages, your furniture and carpets and rugs. Teflon is perhaps the most famous of the PFAS chemicals, but if it was the only prevalent one out there, the chances are that we would not live in a world where 99 percent of Americans have PFAS in their blood. (This is consistent with studies finding that other industrial chemicals, such as plastics, are also in our bodies.)
If the bad news is that PFAS chemicals are everywhere, the worse news is that scientists have long linked them to health problems. Now a new systematic review lends even further weight to the case that PFAS chemicals are bad news, as it reveals that these chemicals are linked to liver disease, too.
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"Systematic reviews are designed to look at all the available scientific evidence to see if there is consensus on the relationship between an exposure and an outcome," corresponding author Liz Costello, MPH and a PhD student at the University of Southern California, told Salon by email. "This is one way to address concerns about limitations or biases that an individual study might have. Someone might dismiss the results of a single study, but when you look at it in the context of all other research on the topic this can be powerful evidence for a real association."
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In the systematic review published by the journal Environmental Health Perspectives, the researchers concluded that there is "consistent evidence for PFAS hepatotoxicity from rodent studies, supported by associations of PFAS and markers of liver function in observational human studies." Because scientists are not allowed to directly experiment with PFAS on humans, they do not know for certain that they are linked to liver disease. The existing body of evidence, however, strongly suggests that this is the case.
"When you're looking at observational studies in humans, you can almost never say with complete certainty that an exposure directly causes a health problem," Costello explained, adding that it would be unethical to do so. "For humans, we can say that the current body of research supports a relationship between higher exposure to certain PFAS chemicals and higher blood levels of ALT. This is also supported by animal research, where you can do experiments that let you control PFAS exposure and other environmental conditions."
Although the study looked at a number of liver enzymes, the review specifically zeroed on a liver enzyme known as ALT, or Alanine Aminotransferease, as it is one of the most common biomarkers they could find in the existing literature.
"ALT is a good indicator of liver injury, but it can't confirm a diagnosis of NAFLD [Nonalcoholic fatty liver disease] or tell us much about the severity of liver disease," Costello wrote to Salon. "To do that, we need more studies that can look at other measures of liver damage and NAFLD (liver biopsies, MRI scans, etc), and that will follow participants over several years."
In light of growing concerns about PFAS chemical contamination, a pair of Democratic legislators introduced a bill to regulate PFAS chemical pollution and outright label two of the chemicals, PFOA and PFOS, as "hazardous" so that the Environmental Protection Agency (EPA) can be authorized to clean up contaminated water utilities and wastewater treatment sites all over the country. President Joe Biden's current EPA administration, Michael Regan, told the Senate during his confirmation hearing that he was going to prioritize regulating PFAS chemicals. Because PFAS chemicals are currently not labeled as "hazardous substances," the EPA is limited in how aggressively it can pursue the task of cleaning them up.
The very nature of PFAS themselves does not help matters.
"It's very difficult for individuals to control their PFAS exposure – PFAS are in so many products (and water, or food) and often we don't even know we are exposed," Costello explained. "Even when older PFAS are phased out and no longer used, newer PFAS chemicals replace them. You won't usually see these listed on a product label. At this point, the focus should be on removing PFAS from products and the environment, and on increasing regulatory efforts to make sure replacement chemicals are safe."
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