Research on Per- and Polyfluoroalkyl Substances (PFAS)
Per- and polyfluoroalkyl substances (PFAS) are a diverse group of compounds resistant to heat, water, and oil. For decades, they have been used in hundreds of industrial applications and consumer products such as carpeting, apparels, upholstery, food paper wrappings, fire-fighting foams and metal plating. PFAS have been found at very low levels both in the environment and in the blood samples of the general U.S. population.
These chemicals are persistent, and resist degradation in the environment. They also bioaccumulate, meaning their concentration increases over time in the blood and organs. At high concentrations, certain PFAS have been linked to adverse health effects in laboratory animals that may reflect associations between exposure to these chemicals and some health problems such as low birth weight, delayed puberty onset, elevated cholesterol levels, and reduced immunologic responses to vaccination.
- Characterizing and Detecting Per- and Polyfluoroalkyl Substances
EPA’s Perfluorooctanoic Acid (PFOA, a type of per- and polyfluoroalkyl substance) Stewardship Program asked companies who make consumer products containing PFOA to voluntarily stop using the chemical in their products.
- Characterizing Fate and Transport of Per- and Polyfluoroalkyl Substances Research
EPA develops methods for characterizing the degradation of fluorotelomer-based polymers (or FTPs) into perfluorooctanoic acid (PFOA) and other Per- and Polyfluoroalkyl substances (PFAS). FTPs are by-products of chemicals manufactured to make consumer products moisture-resistant and stain-resistant. EPA studies whether FTPs degrade to form smaller, more hazardous PFAS products.
FTPs are important products of the chemical manufacturing industry. EPA conducted studies that documented that FTPs degrade in soil to form PFOA and other chemical compounds, adding to the amount of PFAS in the environment. Prior to this research, it was widely held that FTPs did not break down in the environment to form potentially hazardous compounds. EPA scientists have published results that indicate that FTPs do indeed break down over time.
EPA also developed sophisticated laboratory methods to analyze soil, sewage sludge, plants, animal tissue, and water for PFAS and related compounds. These methods have shown that the application of sewage sludge to agricultural land may be a significant source of PFAS exposure to humans. More than half of the sludge produced in the U.S. is applied to agricultural land.
- Research on Ecological Risk from Per- and Polyfluoroalkyl Substances
Certain per- and polyfluoroalkyl substances (PFAS) are regularly found to be contaminants in surface water. Some of these compounds have been found to be toxic in laboratory animals, meaning they could also affect resident fish populations. EPA researchers participate in a collaborative effort to investigate PFAS levels in surface waters and their resident fish populations. Consumption of water and fish containing PFAS are thought to be possible contributors to the amount of PFAS found in humans.
EPA researchers are working to determine the link between the concentrations of PFAS in water and fish populations to investigate the impact of the PFAS on the health of fish populations. The data produced from this research will support policies related to fish consumption, adding to the protection of human health. The data will also be used to compare surface water tested to other waters throughout the nation in an effort to establish ways to mitigate risks.
- Exposure from Per- and Polyfluoroalkyl Substances Research
EPA scientists develop sensitive analytical methods to
- detect Per- and Polyfluoroalkyl Substances (PFAS),
- determine break-down of precursor fluoropolymers into PFAS,
- determine PFAS levels in consumer products, and
- evaluate the relationship between PFAS levels in freshwater and the health of fish populations.
Reliable methods to minimize the discharge of PFAS in the wastewater treatment processes are now available. Researchers work with partners to assess if PFAS can be transferred to edible crops in the field from biosolids laden with these chemicals.
- Per- and Polyfluoroalkyl Substances: Toxicity Research with Animal Models
In the 1980s and 1990s, a few laboratory toxicity studies reported liver toxicity and induction of tumors when animals were exposed to PFAS. At the turn of the century, a study reported that rodents exposed to PFOS (one type of PFAS) during pregnancy caused stillbirth. Biomonitoring studies also indicated high prevalence of PFAS in the blood of workers and the general populations worldwide, as well as in the blood and tissues of wildlife even in the Arctic.
To fully assess the potential human and ecological health risks of these chemicals, EPA conducted research with various laboratory animal models. Exposure to high doses of PFOS in rats and mice during pregnancy caused mortality shortly after birth, likely related to impairment of pulmonary function. At lower doses, newborns survived, but their growth and development were retarded.
Exposure to PFOA in laboratory animal studies did not produce any adverse reproductive or developmental effects, most likely due to the unique ability of the female rats to eliminate this chemical within hours (unlike the males that take weeks). This gender difference in PFOA clearance is absent in humans, rendering the reproductive toxicity data from the rat model difficult to interpret.
Results from a pharmacokinetic study conducted at EPA indicate that both male and female mice eliminated PFOA at about the same rate, making the mouse a more appropriate model for extrapolation to humans. As PFOA body burden built up in the pregnant mice, neonatal mortality (at high doses) and developmental delays (at lower doses) were seen, similar to findings with PFOS. Results generated from these animal studies have been, and will be used as a basis to:
- generate reference doses and health advisory guidelines (for instance, for drinking water and food intake)
- support EPA policy (Consent Agreement with industry), and
- support rule-making decisions (Significant New Use Rules).
- Using Computational Modeling for Per- and Polyfluoroalkyl Substances Research
Computational models provide powerful tools to analyze large and complex sets of data generated from the laboratory to characterize and simulate the biological findings. There are multiple PFAS found in the environment (at least 14) and in humans (at least 4 commonly detected). EPA researchers use computational models to provide estimates to describe and predict the biological effects and characteristics of PFAS.
Several PFAS research projects rely on computational modeling, especially pharmacokinetic simulations.
- Pharmacokinetic simulations demonstrate the fate of a chemical inside of the body, from initial exposure to elimination, and how the body’s absorption, distribution, etc. may alter the chemical compound.
- Simulations estimate how long different PFAS remain in the body after exposure, what tissue compartments these chemicals are likely distributed into, and whether the body burden of these chemicals can be scaled by doses (extent of exposure).
These estimated parameters can be compared among species (for instance, rats vs. mice vs. humans) and genders to lend insights to the varying degrees of how long PFAS stay in the body. Computational models also determine how different PFAS may interact biologically, which is an important consideration because humans and wildlife are exposed to mixtures of PFAS in the real world.
Pharmacokinetic modeling of selected PFAS (carboxylates) indicates that chemical persistence in the body is proportional to the carbon-chain length (a characteristic of the chemical structure). The lower persistence and less toxic effects of short-chain PFAS (such as PFBA) may render these PFBA viable replacements for the long-chain PFAS (such as PFOS and PFOA) in commerce.