Detailed Q&A about PFAS



What are PFAS?

Why are they necessary?
Where are they used?
Why are we concerned with PFAS, instead of other common contaminants like lead?

Polyfluoroalkyl substances (PFAS) are a large family of man-made chemicals. They share in common the fact that all chemical compounds in this family incorporate several atoms of the element fluorine. PFAS are sometimes called PFCs (per- or poly-fluorinated compounds). You might also see specific compounds referred to (e.g., PFOA, PFOS). Two of the chemical compounds in the PFAS family that were the most commonly used and produced are PFOA (also referred to as C8) and PFOS.

Here, we'll use the term PFAS (plural, PFAS) to refer to the larger group of chemicals, unless we are specifically referring to PFOA or PFOS.

PFAS are (or have been) used to make consumer goods resistant to water, grease, or stains, in products like Gore-Tex rain gear, Teflon no-stick cookware, and Scotchguard stain-repellent for carpets or furniture fabric. PFAS are also found in foams used by firefighters to extinguish oil and gas fires. → REFERENCE  BU SPH, PFAS Factsheet → REFERENCE  The New Lead - Perfluorinated Compounds (PFCs) PFAS are only one class of many "emerging contaminants" being studied by public health scientists. They are called "emerging contaminants" because they have largely gone unregulated over years of use, and now a growing body of science indicates that these chemicals are toxic. The emerging contaminants include many very common chemicals in widespread, high-volume use resulting in regular exposure to the general population.

The toxic effects of these chemicals vary. However, many emerging contaminants have been found to have subtle but important health effects, like disruption of normal hormone function. In most cases, the developing fetus and children are most susceptible to these "endocrine disruption" effects. In addition, some emerging contaminants have important effects on the developing brains of the fetus and of children. → REFERENCE  Kristof, 'How Chemicals Affect Us'

Finally, many emerging contaminants—including the PFAS chemicals—are important because they are very persistent in the environment, meaning that they will be present in the air, water, soil, and in humans and animals for many years and decades after we stop producing them. → REFERENCE  EWG, Dirty Dozen Endocrine Disruptors

PFAS have a unique chemistry, related to their unusual ability to function as water barriers and non-stick surfaces. In particular, and unlike many other important toxics, PFAS are water soluble (that is, they can dissolve in water). Therefore, they are commonly found as contaminants in water, including drinking water, and they can be more easily carried into the body and bloodstream than many other toxic chemicals.

PFAS are still a relatively new class of chemical compounds, and we have much more to learn about their health effects. Testing for PFAS can be difficult and expensive, and interpreting the results is challenging. In fact, it is very likely that public health scientists have not yet identified all the PFAS chemicals that are in use—so the story of PFAS contamination is still in its beginning stages.

How are/were we exposed to PFAS?

See also:
How can I tell whether my water has been contaminted?—see #WATER
How can I tell whether there are PFAS in my body?—see #BLOOD

PFAS are now found almost everywhere in our environment, and it is difficult to quantify how much people are exposed to and exactly how they are exposured. For most people in the USA, who are exposed at so-called "background," or "average", levels of contamination, the primary source of exposure is most likely from consuming foods that were wrapped in PFAS-coated packaging. However, people with higher than average exposure are most likely drinking water that has been contaminated with PFAS.


Because PFAS are water soluble, the biggest threat of high exposure is through drinking water. Until recently, we thought that only a few water supplies were vulnerable to contamination from large PFAS emissions—for example, the water systems in Ohio and West Virginia that were contaminated by DuPont's Parkersburg, WV facility. → REFERENCE  THE TEFLON TOXIN: DuPont and the Chemistry of Deception

However, we now know that PFAS contamination is much more common. PFAS have been found in public drinking water supplies serving an estimate 6 million US residents in excess of federally recommended levels for protecting public health In a survey of public drinking water systems nationwide, PFAS were measured in 33 states at the minimum reporting levels required by the US EPA (the government agency with authority to enforce the Safe Drinking Water Act). PFAS have now been found in some of the drinking water supplies in all six New England states. → REFERENCE  'Unsafe levels of toxic chemicals found in drinking water for six million Americans' → REFERENCE  Hu X, et al. (2016) Environ. Sci. Technol. Lett. 3, 344-350 In Bennington, VT, where drinking water contamination led some residents to have had their blood tested for PFAS, the average PFOA levels were nearly five times the national average, with some residents showing levels more than 100 times higher -- far in excess of what the EPA considers safe. → REFERENCE  Bennington blood tests show high PFOA

Contaminated water is most likely to be found near manufacturing facilities that used PFAS, or in areas where PFAS were used in firefighting foams, especially on military bases. The use of firefighting foams in training location results in a large amount of PFAS on the ground, where it can leech into groundwater sources (wells) or run off into surface water sources (streams, rivers, reservoirs).


Because of PFAS are persistent in the environment, remaining for years or decades without breaking down, they are capable of traveling long distances, especially in water, and may be found far from the locations where they were initially released into the environment.

The specific chemical properties of PFAS cause them to stay in the human body for a long time—many years. This "bioaccumulation" means that even relatively low exposures to PFAS can, over time, lead to very high levels in the blood and tissues. (The same is true with many other chemical compounds, like PCBs, flame retardants, or most famously, DDT.) In addition, people people who are exposed to PFAS are often exposed to a mix of PFAS chemicals. Once in the body, they may be transformed into more or less toxic forms of PFAS. Scientists are also finding that some related chemicals can become PFAS when they enter the body.

In addition to deliberate and accidental pollution from industry, and runoff from firefighting foams, PFAS may enter the environment in many other ways. For example, washing a rain jacket that is coated with PFAS-based water repellents will remove some of this coating, and send the PFAS into the wastewater stream. Although the amount released this way seems small, the widespread use, high persistence, and bioaccumulating properties of PFAS chemicals means that these small amounts can add up and last for a very long time. Once in the environment, they might have effects on plants and animals. They can also then enter the food chain and lead to later human exposure.


PFAS (and related chemicals) are found in many food packaging materials, including microwave popcorn bags and pizza boxes. As with other toxic chemicals, there is usually no requirement for labeling PFAS-containing products, so it is difficult for the consumer to avoid them.

Eating fish caught in contaminated waters may be another significant route of PFAS exposure.

Because PFAS contamination in the environment is so widespread, it is also likely to be found at low levels in meat and dairy products, even far from contamination sources.


Finally, workers in facilities using PFOA and PFOS may be (or may have been) highly exposed to PFOA, PFOS, and related chemicals. This exposure might come from inhaling PFAS chemicals directly, or absorbing them through the skin, or even ingesting them (for example, when eating with PFAS-contaminated hands).


Given their widespread use over many decades, it is no surprise that today nearly all people living in the US who are tested have at least low levels of PFAS in their blood, and some have much higher levels. → REFERENCE  'Unsafe levels of toxic chemicals found in drinking water for six million Americans'

Because of the persistence and bioaccumulation of PFAS, even people who don't use PFAS chemicals, and who live far from contaminated sites, can still be exposed through diet and water. Although the average exposures experienced by the general population are sometimes referred to as "background" levels, there is nothing natural or even safe about them, since PFAS were not present before humans started manufacturing them.

In communities with contaminated water supplies, however, PFAS levels are far higher than "background". That exposure is seen by many as an involuntary intrusion into their bodies. This is referred to as "toxic trespass"—the idea that a polluter is trespassing on your body by introducing toxic chemicals without your consent, and which you don't know about, didn't agree to, and may not even use. → REFERENCE  Sandra Steingraber's War on Toxic Trespassers

Now that we know that many people are exposed, our next task is to figure out what health effects that exposure might cause. For that topic, see #effects.

How do PFAS travel through the environment?

Is PFC contamination ongoing, or has it been stopped?
What are the implications of PFAS contamination for new water sources?

Because PFAS are water soluble, the biggest threat of high exposure is through drinking water. Until recently, we thought that only a few water supplies were vulnerable to contamination from large PFAS emissions — for example, the water systems in Ohio and West Virginia that were contaminated on a very large scale by DuPont's Parkersburg, WV facility.

Today, we're finding that many sources can contribute to PFAS in lakes, rivers, or underground aquifers. In some areas, the largest source is when firefighting chemicals, which often contain PFAS, are allowed to run off onto the ground or into a stream. This may not sound like a major source, but firefighter training can use huge volumes of these substances over and over at the same spot — a training facility or an airport, for example. These PFAS-containing foams can then leach into water supplies, contaminating them.

Since PFAS are used for many purposes, there are other, usually smaller, sources. For example, clothes treated with PFAS will leech more PFAS out into the sewer -- and possibly into the groundwater — with every laundry cycle. (Breathable water-proof or water-resistant fabrics are most often treated with PFAS.)

PFAS chemicals are very persistent in the environment, and won't easily break down. This means that once contamination has occurred, the water supply will likely be contaminated for many years to come.

PFOA and PFOS, historically the two most important PFAS chemicals, are no longer made in the USA. However, there are a great many related compounds with similar properties, which may be use Furthermore, stocks of PFAS firefighting foams can be stored for decades, and are likely to be used in firefighting training long into the future, providing future sources of contamination.

What do we know about the health effects of PFAS exposure?

How strong is the scientific link between exposure to PFAS and health outcomes?
Where do PFOAs accumulate in the body?
Why do PFAS show up in some people more than others?

We know that most people living in the US are exposed to at least some level of PFAS chemicals—and many of us are highly exposed. (See #exposed.) But what are the effects of those chemicals on people?

As is the case with many other "emerging contaminants," PFAS have been in use for a long time—many decades, in the case of PFOA and PFOS—but we are only now learning about their health effects. This problem of "using before understanding" occurs regularly because the US does not require testing of most new chemicals before they are used commercially. (For more on the problem of regulating emerging contaminants, see #future.)

The federal Agency For Toxic Substances and Disease Registry lists these health effects as potentially being associated with PFAS exposure in humans: → REFERENCE  Agency For Toxic Substances and Disease Registry, Health Effects of PFAS

Developmental delays in the fetus and child, including possible changes in growth, learning, and behavior;
Decreased fertility and changes to the body's natural hormones;
Increased cholesterol;
Changes to the immune system;
Increased uric acid levels;
Changes in liver enzymes;
Prostate, kidney, and testicular cancer.

Not all of these effects will necessarily lead to disease; changes in liver enzymes may never lead to a liver disease, for example. So there is still uncertainty regarding the significance of some of these changes. However, other effects (e.g., cancers) represent clearer risks. It's also important to note that not everyone is equally susceptible to these effects. For example, developing fetuses and children are much more susceptible to the endocrine disrupting effects on the thyroid, the brain, and the immune system, since those hormonal systems are still being formed and are especially sensitive during development.


Our strongest evidence for the effects of chemicals is from studying people who are exposed. The study of causes of illness in humans is called epidemiology.

Of course, we can't test dangerous chemicals directly on people. Instead, we look for people and communities who are already exposed—what scientists sometimes call "natural experiments"—and compare them with those who are not exposed to see if we can find differences in their health outcomes. We search for a difference in the health of these populations that can only be explained by the exposure of interest (in this case, PFAS). Unfortunately, epidemiology is extremely difficult and expensive, often requiring a great deal of information about thousands of people over many years to see strong patterns of disease and be able to attribute the disease to the exposure. More importantly, because each of us is so different, because we are each exposed to so many different chemicals, many of which can cause the same or similar diseases, it is nearly impossible to separate out the effects of just one chemical or class of chemicals.

This means that epidemiology is usually not a very sensitive tool for investigating health effects of low-level exposures. In fact, one prominent epidemiologist has defined a disaster as "an event so severe that even an epidemiologist can detect it." → REFERENCE  Ozonoff, quoted in Wartenberg, Exposure Science: A Tool for Assessing Public Health Impact

Several large groups of people exposed to PFAS—"cohorts"—have now been studied. The largest cohort, centered around the Ohio River near Parkersburg, WV, was exposed to PFOA in their drinking water over several decades, as the DuPont facility there emitted that chemicals into the air and water. The study, led by the C8 Science Panel → REFERENCE  C8 Science Panel website , was undertaken after a lawsuit against DuPont, and led by by three neutral epidemiologists appointed by the court. ("C8" is another term for PFOA.) (As an example of the difficulty and expense of large-scale epidemiology, the C8 study took seven years and cost $35 million dollars.)

At the conclusion of the study, the C8 Science Panel reported to the judge that they had found "probable links" between PFAS exposure and cancer, thyroid disease, high cholesterol, ulcerative colitis, and pregnancy-induced hypertension. → REFERENCE  C8 Science Panel: Probable Link Reports Although these "probable links" represent a legal conclusion rather than a traditional scientific one, they summarize most of the best data available to epidemiologists by 2013. The Science Panel did not find a "probable link" for many other outcomes, e.g., neurodevelopmental disorders in children, birth defects, low birth weight. Other epidemiologic studies have broadly confirmed the findings of the C8 Science Panel. However, it won't be surprising if future studies are able to identify health effects that the C8 Science Panel was not. Very rarely in the history of science has a single study set the standard for what is considered general knowledge. DATA FROM ANIMALS

Since human data on the effects of PFAS is so limited, and so difficult to collect, we also study the effects of these chemicals on animals.

In animal studies, PFAS have been shown to have adverse effects on multiple organs, to cause developmental problems to offspring, to reduce immune function, and to disrupt normal endocrine activity.

Once PFAS are in the body, they will remain until they are excreted in urine or feces over a period of many years.


Many of the body's functions are regulated by the glands and hormones that make up the endocrine system. It takes only tiny amounts of these hormones—hormones like estrogen, testosterone, thyroid hormone, insulin, and many others—to control the development and actions of the rest of the body.

A number of manufactured chemicals can mimic one or more hormones; that is, the chemical may look enough like a specific hormone that it can trigger the response of the endocrine system. For example, the well-known chemical bisphenol A (or BPA) can bind to estrogen receptors, tricking the body into thinking that there is more—or less—estrogen than is actually present. Because hormones are used in very small amounts to send signals through the body, very low levels of these endocrine-disrupting chemicals (EDCs) can have large effects. This is especially true when hormonal systems, like the thyroid or the reproductive system, is developing during pregnancy and through puberty.

Some PFAS chemicals, notable PFOA, show evidence of endocrine-disrupting effects in lab animals and in humans. PFOA has been shown to modulate the effects of a specific hormone-sensing molecule, called PPARα, but is likely to have effects on other hormone systems as well. → REFERENCE  Endocrine disrupting properties of perfluorooctanoic acid One epidemiologic study found a nearly three-fold risk of overweight/obesity in daughters of women highly exposed to PFOA; this is likely related to the hormone-mimicking effects of PFOA on PPARα, although it may also be related to PFOA's thyroid effects. → REFERENCE  Halldorsson et al. 2012. Prenatal Exposure to Perfluorooctanoate and Risk of Overweight at 20 Years of Age: A Prospective Cohort Study A laboratory study in rats indicates that PFOS can affect the way the brain uses hormones to help regulate other organ systems. → REFERENCE  US EPA, Emerging Contaminants - Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA), March 2014

If you found these examples confusing or uncertain, you are not alone. Endocrine disruption is a subtle and difficult subject to study. For the moment, it is clear that PFAS chemicals appear to interfere with at least several different hormone systems. Research in this field will be ongoing for some time to come.


For many toxicants, we can identify populations who are at especially high risk. For example, as we have noted above, children (and fetuses in utero) are more susceptible to developmental effects, especially through endocrine disruption. The thyroid, for example, helps control growth and metabolism, and these processes could be altered by PFOA's effects on thyroid hormone.

Unfortunately, kids also tend to have higher levels of PFAS exposure than adults do. This might be due to higher exposures (for example, if a kid's diet has more PFAS in packaging materials), or it might be biological (for example, if kids don't metabolize and excrete PFAS as well as adults).

While some people might be more biologically susceptible to toxins like PFAS, there can also be social or behavioral reasons that a particular group might be subjected to unusually high levels of exposure. For example, studies have shown that communities of color are more likely to be burdened by toxic emissions; moreover, the siting of the polluting facilities is partly determined by the presence of those communities of color. → REFERENCE  Morello-Frosch et al. (2002), Environmental justice and regional inequality in southern California: implications for future research This type of problem, which has been termed environmental racism, plays an important role in the unequal exposure to toxics in the United States. (The relationship of PFAS contamination to race, income, and other social factors has not yet been studied.)

What is still unknown about the risks of PFAS?

PFAS is a large class of chemicals that includes many related compounds. Only PFOA and PFAS have been even moderately well studied thus far.

We are really just getting started learning about the effects of PFAS. In fact, we know there are specific PFAS chemicals already in widespread use that scientists haven't even identified, never mind studied. This is a serious problem with our chemical regulatory system: See #future.

If PFAS are hazardous, how are they regulated?

Now that we know about the contamination, are we still being exposed?

Although PFAS have been in use for decades—and although public health scientists have expressed concerns about them for many years—they have been essentially unregulated until recently.

The US regulatory system does not generally require any testing before new chemicals can be used. Furthermore, in most cases, chemicals cannot be regulated until they are proven to be toxic.

The presence of several large contamination incidents has now created enough public awareness that manufacturers have now voluntarily stopped making the most heavily-used PFAS chemicals. (These chemicals may still be used abroad, however, and these products are still imported to US.) Unfortunately, in most cases, we don't yet know what chemicals are being used to replace them, althought it is very likely that most of the replacements are also PFAS chemicals.

This demonstrates a serious imbalance between government and industry: Manufacturers can change their products at will, but EPA is required to accumulate many years of scientific evidence before regulating a new chemical.

As one scientist recently pointed out, we know that there are PFAS being used out there that we haven't even yet identified!

In November 2016, EPA issued a health advisory for PFOA and PFOS, setting guidance for permissible limits of these chemicals in drinking water. → REFERENCE  US EPA, Drinking Water Health Advisories for PFOA and PFOS

See #safe for details.
For more about regulating chemicals like PFAS, see #future

Is there a test for PFAS contamination in my water?

Where has water been tested?
Can we test the water ourselves?

See also, Should I #filter my water?

Testing water for PFAS contamination is possible, although because PFAS chemicals are so widespread, even collecting a sample to be tested can be a difficult process. While costs vary widely, a test for PFAS in water will cost several hundred dollars.

US EPA Method 537 → REFERENCE  US EPA, Determination of Selected Perfluorinated Alkyl Acids in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS) specifies the collection and testing process in great detail, and this process should be followed if results will be used in any official or legal process. While Method 537 provides information on testing for a number of PFAS, it does not test for all of them. Some test facilities may report only PFOA, or PFOA and PFOS, or another limited set of PFAS.

The good news is that, if you are on a public water system, your system managers are responsible for this testing. They may already have test results, or may be able to get them.

If you receive water from a public supply, your water utility is required to provide you with an annual Consumer Confidence Report describing what tests have been performed, and explaining any cases in which the water failed federal water quality requirements. You can find your Consumer Confidence Report through the EPA's search tool, or just try searching for your town's name and the phrase "water quality report" or similar keywords. Check your water system's CCR to find out what levels were measured in your local system, and when and where.

If you're on a well, ask your regular water testing service about testing for PFAS. Be sure to follow up with your local and state departments of health and environment to make sure they are aware of your concerns. In some cases, they may be able to connect you with other resources. If your groundwater is contaminated, it is likely that the whole aquifer—the underground body of water your well draws from—is also contaminated; so it is important that others know about your results.

The New Hampshire Department of Environmental Services has a list of labs that test for PFAS, as well as some laboratory testing guidelines. (Note: Toxics Action Center and the Boston University Superfund Research Program have no experience with these labs, and do not endorse any specific lab.))

For details on how to interpret test results, see #interpret
For the question of what level of PFAS contamation is "safe", see #safe
For information about treating water and reducing your PFAS exposure, see #reduce

Can I have my blood tested for PFAS? Should I/we be tested?

Testing for PFAS in blood is difficult and expensive, and can only be done by a small number of laboratories.

Before testing for PFAS in blood, it may be more useful to identify the sources of the PFAS—for example, by determining whether your drinking water is contaminated. If that's the case, you'll have better information about how you were exposed, and how you can reduce your exposure.

Unfortunately, if you have elevated levels of PFAS in your blood, there is nothing that can be done to remove the PFAS. The best thing you can do is to identify the source of your exposure, and prevent further exposure.

To learn how to reduce your future PFAS exposure, see #reduce.

If you are concerned about PFAS exposure through contaminated water in your community, make sure you've tested your water supply first, and investigated possible sources of contamination. If you can show that you are exposed to PFAS in your water, that may be all you need to know. If you're exposed above the "safe" level, your local government should be taking steps to reduce the contamination. Even if your water is contaminated below a "safe" level, you should still be able to pressure your local government and water supplier to reduce the contamination. Proving that the PFAS is also in your blood may not be necessary.

For information on testing of PFAS in water, see #water
For information on what level of PFAS contamination is "safe", see #safe

If your community has been exposed to high levels of PFAS, your local department of health may be able to put together a blood testing program. Contact your local or state health agency and ask about having your community tested.

If your department of health is not offering blood tests for PFAS, and if you have reason to be especially concerned about your PFAS exposure, talk to your healthcare provider about a blood test. However, this test may be quite expensive, and will probably not be covered by your medical insurance.

One final caution: Test methods for the most common PFAS chemicals, especially PFOA and PFOA, are well established. However, tests for other PFAS chemicals may be less common or more difficult. If you are concerned about a specific PFAS chemical, make sure that one will be analyzed. It isn't possible to test a sample for all chemicals; chemists typically need to know which specific ones they are looking for.

For information about interpreting your blood test results, see #interpret

Several large-scale testing programs have been done in response to specific contamination incidents. To get a sense of what is required, see Vermont's PFOA blood testing program → REFERENCE  Vermont's PFOA blood testing program and the C8 Science Panel's medical monitoring program. → REFERENCE  C8 Science Panel screening program

My test showed that I have PFAS in my blood. How should I interpret this result?

The extremely widespread use of PFAS means that almost all Americans now have PFAS in their bodies and in their blood. As test methods become more sensitive, we are able to find PFAS at lower and lower levels. Currently, about 99% of Americans tested have detectable levels of PFAS in their blood. Remember, a detectable level of PFAS does not indicate a specific health concern or health risk.

The US federal government's National Health and Nutrition Examination Survey (NHANES) provides a great deal of data on PFAS levels in blood, so anyone can compare their specific results with results from others. This will give you a sense for whether your specific PFAS exposure is high, or medium, or at the "background" level of average everyday exposure. We will discuss this data at #compare below.

Comparing to other people is useful in giving your context about whether your exposure is high or low, in comparison with other who have been tested. But we don't know enough about PFAS to connect any amount in blood with specific health problems, so the blood test itself won't tell you about any specific health concerns that may relate to PFAS exposure now or in the future. Some people might have relatively high amounts of PFAS in their blood, but not have health effects from PFAS, while others might be more susceptible. For example, developing children and fetuses are more susceptible to the endocrine disrupting effects on the thyroid, the brain, or the immune system, since those hormonal systems are still being formed and are especially sensitive. Unfortunately, kids also tend to have higher levels of PFAS exposure than adults do. This might be due to higher exposures (for example, if a kid's diet has more PFAS in packaging materials), or it might be biological (for example, if kids don't metabolize and excrete PFAS as well as adults).

The best thing you can do is to reduce any continued exposure to yourself, your family, and your community. Also, let's try to fix our broken chemical regulatory system so that this problem doesn't happen again. See #future.

Much more detail about the terminology used in interpreting your results is available in the longer answer to this question.


When interpreting your blood test results, look at your own value and compare it to the range and the median in your community and in other communities studied. If you are given a percentile for your results, that may be the most useful measure to see where you stand among your community members.

The glossary of terms below may help with understanding your results and comparing your results to others'. We'll also show you some data on exposure levels in different groups, to help you compare your PFAS concentrations to other people.


PFAS concentrations in water are typically measured in one of the following units:
ppb: parts-per-million: 1 ppm is equal to one gram of PFAS in one million grams of water.
ppb: parts-per-billion: 1 ppb is equal to one gram of PFAS in one billion grams of water.
ppt: parts-per-trillion: 1 ppt is equal to one gram of PFAS in one trillion grams of water.

Note that 1000 ppt = 1 pbb (and 1000 ppb = 1 ppm). Therefore, EPA's guideline for PFAS in drinking water can be expressed as 70 ppt or as 0.070 ppb.

When intepreting your drinking water results, keep in mind that there is no simple connection between your water PFAS levels and your blood PFAS levels. High levels of PFAS in water are likely to contribute to your body burden, but other sources, and individual factors, can also influence your body burden of PFAS.


PFAS in blood are most commonly measured in units of
  μg/L—micrograms of PFAS per liter of blood; or
  ng/mL—nanograms of PFAS per milliliter of blood

Conveniently, μg/L and ng/mL work out to be the same units! So if your test result tells you that you have 58 μg/L, you may also read that as 58 ng/mL—the two units mean the same thing. Don't get concentrations in drinking water confused with concentrations in blood! Fortunately, they are usually referred to by the different units described above.

See below for information on comparing your water and blood results with others'.
For the question of how much is too much, see #safe.


Your lab reports may use some of the following terms. If you have trouble interpreting your results, or you have other questions, contact Toxics Action Center.

PERCENTILES are often used to indicate how your result compares to other people's. Your percentile tells you how much of the population has blood concentrations lower than yours. (You may be familiar with percentiles from standardized testing and other uses.)

For example, if you are in the 94% percentile, your blood concentration is higher than 94% of the population: In this case, you would seem to be fairly highly exposed. If you are in the 25% percentile, however, most of the population -- about 75%—has higher blood concentrations than you do.

The MEDIAN concentration is the 50% percentile. That is, half of the population has concentrations above the median, and half has concentrations below the median. If you are at the median concentration, you have very "average" concentrations. Remember, this doesn't tell you whether you are or are not at risk!

The MEAN is the "average" in the usual sense of the term. For our purposes, the MEAN is much less useful than the MEDIAN, because one very high or very low result can change the mean dramatically (but will not affect the median).

The GEOMETRIC MEAN (or GEOMEAN) is another way of calculating the mean for some types of data. This is more useful than the MEAN for our purposes; however, the GEOMETRIC MEAN can still be affected by a single very high or low data point.

The RANGE simply tells us the highest and lowest values in the data. If the RANGE is 12 to 98 ng/g, the most exposed person has 98 ng/g in their blood.

The LEVEL OF DETECTION (or LOD) corresponds to the lowest concentration of PFAS that the laboratory can measure. For example, if the LOD is 0.1 ng/g, this means that the lab cannot detect PFAS below 0.1 ng/g. If your blood concentration is lower than the LOD, the report will most often say "<LOD" or "<0.1 ng/g" to indicate that your specific level is undetectably low. (The lab won't usually report a "0", because you might have a very small amount that is too small to be detected.) Different laboratories and different methods will have different levels of detection.


The best data on background levels of chemicals in people living in America comes from the federal government's National Health and Nutrition Examination Survey (NHANES), and is described in the very detailed National Report on Human Exposure to Environmental Chemicals.

In 2011-2012, the geometric mean of blood PFOA concentrations—a good measure of the average exposure for this type of data—was 2.08 μg/L. The 95% percentile was 5.68 μg/L; that is, 95% of the population had less than 5.68 μg/L of PFOA in their blood. → REFERENCE  Fourth National Report on Human Exposure to Environmental Chemicals (updated January 2017). A sketch of this distribution is shown below. By comparison, a sample of residents of Hoosick Falls, NY, where the drinking water was contaminated with PFOA, found a geometric mean of 23.5 μg/L. Notice that this "average" value in Hoosick Falls residents is far higher than even the 95th percentile of the NHANES (background) data; in fact, it is too high to fit on our chart above.

What is the safe level of PFAS exposure?

How concerned should we be about PFAS in our water or our blood?

When we talk about "safe levels" of exposure, it is critical to distinguish between blood levels and drinking water levels. Someone with a "safe" level of PFAS in their water might still have high levels of PFAS in their blood. In fact, the scientific data indicates that most Americans get the majority of their PFAS exposure from sources other than drinking water.

Unfortunately, we simply don't know enough about the toxicity of PFAS to determine whether a certain amount of PFAS in blood is "safe". The best you can do with blood results is to compare them with others' to see if yours are elevated—see #interpret for more information.

If you receive water from a public supply, your water utility is required to provide you with an annual Consumer Confidence Report describing what tests have been performed, and explaining any cases in which the water failed federal water quality requirements. You can most often find your Consumer Confidence Report online—try searching for your town's name and the phrase "water quality report" or similar keywords.

In November 2016, EPA issued a health advisory for PFOA and PFOS. For more information about this health advisory, see the longer answer to this question. EPA's health advisory sets a maximum of 70 ppt (parts-per-trillion) for the combined concentration of PFOA and PFOS in drinking water. → REFERENCE  US EPA, Drinking Water Health Advisories for PFOA and PFOS

For the definition of "ppt" and other terms, see #interpret.

However, some experts have critized EPA's standard as permitting too much PFAS in drinking water. The environmental advocacy organization Environmental Working Group has argued that the standard should be ten times lower—ten times more protective—at about 7 ppt. → REFERENCE  Environmental Working Group, Teflon Chemical Harmful at Smallest Doses

Other governments have set different thresholds for the maximum amount of PFAS allowed in water. For example, the Vermont Department of Health has set its drinking water health advisory level at 20 parts per trillion (20 ppt), far lower—and therefore more protective—than the US EPA's standard. → REFERENCE  Vermont Department of Environmental Conservation, Interim PFOA and PFOS Standards

Check your water system's CCR to find out what levels were measured in your local system, and when and where. See #water for more information.

Note: EPA's health advisory refers to PFOA and PFOS because these two chemicals have been most heavily studied—but EPA has not set limits for other PFAS chemicals, although many are likely to have similar effects.

Do you think other PFAS should be regulated as well? See #future.

These numbers—whether EPA's advisory value of 70 ppt, or the lower levels of 7 ppt suggested by EWG—seem very small! But remember, PFAS—like many other industrial chemicals -- accumulate in the body, and are only slowly excreted. Your body and blood concentrations of PFAS are likely to be significantly higher than the concentration in the water you drink!

Some critics suggest that concentrations of chemicals in the parts-per-billion (ppb) or parts-per-trillion (ppt) range are too small to have an effect on the body. But health effects are all about having the right molecules in the right places—and even a small number of molecules can be important. To take one example, Viagra causes its famous effects at a blood concentration of about 3 ppb Similarly, very small concentrations of toxins can have important effects, especially on susceptible populations.

What can I do to reduce PFAS exposure and to lower my health risks?

Can I reduce the amount of PFAS already in my body?
How can I reduce future exposures?
Is it safe to shower/bathe in PFAS-contaminated water?
What about food and food packaging?

For specific details on water filtration, see #filter below.

After decades of production and use, about 99% of Americans tested now have detectable levels of PFAS in their blood. Remember, a detectable level of PFAS does not indicate a specific health concern or health risk.


The body will naturally metabolize and excrete PFAS over time. However, this is a very slow process: It is estimated to take 2-4 years to eliminate half of the PFOA from the body. There is no proven way to speed up this elimination of PFAS chemicals from the body. "Toxic eliminating" diets or supplements are not likely to have any effect on PFAS levels.

The persistence of PFAS is one reason why preventing future exposure is so important. For details about how to lower your exposure to PFAS in drinking water, see the longer answer to this question.

Note: A handful of the most hazardous toxicants can sometimes be removed medically; for example, chelation therapy can remove lead from blood. However, these methods are very difficult and extremely invasive, and are only last-ditch approaches to be used in the most extreme cases under careful medical supervision. There is no such approach to lowering PFAS already in the blood.

Overall, preventing future PFAS exposure to yourself, your family, and your community is the best way to avert further health impacts.

Of course, paying attention to proper diet and exercise are the very best things you can do to improve your overall health and to reduce health risks.


The best thing that you can do right now is to reduce further exposure to PFAS. First, find out about PFOA in your drinking water sources. If you are on a public water supply, your water utility is responsible for making sure your water meets federal and state criteria. See #water for details about having your water system tested. If you are on a private well, you may have to have the water tested yourself. See #water for details. Be sure to follow up with your local and state departments of health and environment to make sure they are aware of your concerns. In some cases, they may be able to connect you with other resources.


Contaminated water can be treated at home by water filters only if they are specifically designed to remove PFAS. Most commercial water filters are not.

For more information, see #filter.

Is it safe to shower/bathe in PFAS-contaminated water?



Other sources of PFAS can be significant for some people. PFOA, other PFAS, and related chemicals can be found in many food packaging materials, including microwave popcorn bags and pizza boxes. (These chemicals are useful because they prevent oils and greases from binding to the packaging material.)

If you rely on a lot of packaged food, you might want to ask your local groceries or the food manufacturers whether they use PFAS (and other toxic chemicals). Although they may not be able to tell you, and they may not even know, this is one small way to raise awareness of the problem.

Finally, if your local rivers or streams are known to be polluted with PFAS, fish caught in those water bodies might also be polluted. If this is the case, consider practicing catch-and-release fishing instead of eating your catch. Call your local and state departments of the environment, or your fish and game agency, and ask about having fish tested for PFAS.

Should I filter my water?

Do commercial filters (e.g. Brita) work for PFAS and other emerging contaminants?
Does boiling water help eliminate PFAS?
Is distilled water safe from PFAS?
Is bottled water safe from PFOA?

Contaminated water can be treated at home by water filters only if they are specifically designed to remove PFAS. Most commercial water filters are not.


Many people see bottled water as a solution—and in cases where the water system is known to be contaminated, it may be necessary. However, bottled water is very poorly regulated. In addition, the environmental footprint of transporting bottled water, and of bottle waste—almost always plastic—is very high. In cases where PFAS contamination can be treated at the source, drinking clear tap water, perhaps treated with a simple activated carbon filter, is usually the most environmentally sound and healthiest approach.

Boiling water is useful to kill living parasites— including bacteria and viruses—in contaminated drinking water. However, this approach isn't effective with most toxics. PFAS is quite stable and persistent, and boiling water is unlikely to remove any significant amount of it.

While filtration may be useful, the best approach for significantly contaminated water will be to make sure your water supplier manages contamination of the aquifer at the source. See #reduce and #water for more information.

How can my community respond to this contamination?

First, get informed!

If you know or suspect that your community's water has been contaminated with PFAS, a good starting place is to get your #water tested. Be sure to check the #CCR published by your water supplier for information on what testing they've already done. If your water supply is not testing for PFAS, pressure your local government to have the water tested. If your water is contaminated, be sure your state and local health officials know about the problem. If the contamination is below the EPA's #advisory, they may not be willing (or required) to act. However, check guidance from other states and localities to see if you exceed guidelines set elsewhere.

It's important to identify the source of contamination. Are there major sources—for example, heavy use of fire-fighting foams—in your area? If the source is not already known, your state and local health officials may be able to help you track it down. If your water is contaminated, you may want to have your #blood tested as well. Remember, testing—especially blood testing—is expensive. Talk to your state and local officials about setting up a monitoring program.

Get organized!

You can't respond to contamination alone—you'll need the help of your neighbors and friends, as well as scientists and government officials. You need to organize! A number of resources exist to help your community get organized to fight pollution. If you know of groups in your area, contact them and ask for help. You can always contact Toxics Action Center for connections and next steps.

In addition to organizing help, you may need expert assistance to help your community understand their contamination, the possible effects, and the best ways to respond. Consider contacting local colleges and universities (especially schools of public health) for assistance. Toxics Action Center, and other that focus on community health and environmental justice, should also be able to connect you with scientists who can help.

Is a health study right for your community?

Many communities immediately decide that they need the state to perform a health study of their community to evaluate the effect of the pollution. While a health study can provide important information, it might also prove inconclusive, and in either case it is likely to take a substantial investment of time and resources.

If you've done the basic background work above, and you think that a health study is the right next step, see our guide, Is a Health Study Right for Your Community?. This guide will help you establish your research question and develop the best study to answer your community's questions.

How can we make sure contamination like this doesn't happen in the future?

What can we do to promote responsible chemical use & development?
How can chemists find safer chemicals?
Are the C6 chemicals good replacements for the C8 PFAS chemicals

The current situation—in which millions of Americans are exposed to PFOA, PFOS, and probably to other PFAS in their drinking water—should never have happened. → REFERENCE  'Unsafe levels of toxic chemicals found in drinking water for six million Americans'

It happened because we allowed a chemical to be used widely and at high volumes before we had adequately tested it. This is not an isolated incident or a one-time occurance. The same thing happened with leaded gasoline, and with lead in paint. The same thing happened with flame retardants and with bisphenol A. Incidents like these, and many more, happen because of the design of the US regulatory system, which over the past 40 years has not required companies to test chemicals before using them. (This situation may now be changing; see below for information on changes to federal regulations.)

By contrast, European chemicals regulation requires extensive testing for human and environmental health effects before a chemical can be placed on the market—summed up in the simple phrase, "no data, no market".

The difference between these two systems lies in who has the burden of proof. In Europe, a chemical manufacturer must prove a chemical safe before it is used. In the US, the government must prove that a chemical is harmful before its use can be stopped. The response to concerns about PFOA contamination has followed the usual path. As chemicals come under scrutiny, and start being studied for their health effects, manufacturers typically stop dumping the chemicals, preferring to dispose of them more responsibly or to recycle them. For example, Dupont's contamination of the air and water around its Parkersburg, WV facility had been going on for decades before 1999, when a a WV farmer sued the company alleging that the company's PFOA emissions had sickened his cows. → REFERENCE  THE TEFLON TOXIN: DuPont and the Chemistry of Deception Within a few years, under intense public scrutiny, Dupont dramatically reduced its emissions. As we have learned more about the effects of PFOA and PFOS, they have been used less and less. By 2013, DuPont it had eliminated the use of PFOA altogether—without the chemical having been regulated. In some cases, EPA will negotiate an end to production with a company rather than attempting to pass a contentious new regulation.

Today, we know much more about the effects of PFOA and PFOS, and EPA has now set standards for drinking water (see #safe). This appears to be a successful end to the PFOA/PFOS story—and it certainly is an improvement—but this approach really underscores the EPA's lack of authority to regulate chemicals of concern. Halting production of PFOA doesn't end consumer exposure, since PFOA and PFOA-containing products can still be imported, and since these chemicals will remain in the environment long after they have been released.


It's important to note that the PFOA/PFOS health advisories address only past contamination by these two known PFAS chemicals. As they phased out PFOS/PFOA, manufacturers started using alternative or substitute chemicals in their place. But these substitutes may be entirely new and completely unstudied molecules. Even their specific identity is often protected as confidential business information; therefore, it can't be studied by researchers outside the industry. Scientists sometimes call this process "regrettable substitution", as it's quite possible that the new chemical might be as bad as the one we phased out.

Indeed, finding alternatives to dangerous chemicals is a serious challenge. Let's take the example of BPA ("bisphenol A"), a name you probably recognize know from seeing "BPA-free" labels on water bottles. "BPA-free" sounds great, right? But what the label doesn't tell you is what chemical is used instead of BPA, and whether that chemical is any safer. In some cases, the alternative to BPA is BPS or "bisphenol S"—a chemical which has only recently been studied, but which appears to have similar toxic effects as its close cousin BPA. Have we made any progress?

In the case of PFAS chemicals like PFOA and PFOS, some scientists are now concerned that companies are switching to the "C6" chemicals. These perfluorinated chemicals have six carbons, instead of the eight carbons in PFOA or PFOS, but otherwise are very similar to their bigger cousins. In fact, the C6 chemicals are likely to be more soluble in water, to move more easily through the environment, and to be taken more readily into the human body.

Scientists know very little about the C6 chemicals; but it is quite likely that some companies are already using them today. Someday soon, you may see a label on your water-repellent jacket that says "no PFOA or PFOS"—but you won't know whether they are using C8, or a new C6 chemical, or some completely different (and possibly unstudied!) chemical.


We have limited information about PFOA and PFOS — but we have much less information about other PFAS! In fact, experts consider it almost certain that there are specific PFAS chemicals in use that we haven't even identified, never mind studied. And even when we've addressed the existing set of PFAS chemicals, there are certain to be new ones—for example, the short-chain "C6" chemicals—that will enter commerce over the next few years. If we don't learn from our mistakes now, we could face the same problem with those in the future.