November 3, 2023

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What Frogs, Toads, and Salamanders Can Teach Us about PFAS Toxicology

Geosyntec condenses 16 Purdue University studies into easy-to-reference PFAS screening levels for environmental managers

How much PFAS does it take to be toxic to people and animals?

Over the past six years, the United States Department of Defense’s Strategic Environmental Research Development Program funded a study by a research team at Purdue University to get closer to that answer. To do this, the Purdue team evaluated the ecotoxicological effects of PFAS on amphibians at sites with these compounds.

Recently, Geosyntec's Zach Pandelides and Jason Conder used the Purdue team's research to develop screening criteria that regulators, airports, and site owners can use to conduct more efficient PFAS investigations. Their work was recently published in Environmental Toxicology and Chemistry.

Below, Zach and Jason discuss amphibians, PFAS toxicology, and how this recent research can be applied to set PFAS thresholds and make informed decisions.

About the Speakers

Jason Conder, PhD, IBERAD, is a principal scientist with more than 15 years of experience addressing contaminated sites and environmental risks. An internationally recognized expert on PFAS, Jason has conducted product- and site-specific PFAS fate and risk assessments and formulated guidance for the US Department of Defense, including a PFAS "Frequently Asked Questions" document and guidance on PFAS ecological risk assessment.

Zach Pandelides, PhD, is a senior staff scientist who specializes in environmental risk assessment and sediment and water quality assessment. He has coauthored more than 10 peer-reviewed articles in environmental toxicology, chemistry, and molecular biology, and has presented technical work at numerous scientific conferences. His recent work has involved ecological risk assessment to PFAS and microplastics.

Q & A

What was Geosyntec's role on this project?

Zach Pandelides
The Department of Defense tasked us with distilling Purdue’s great work into guidelines that their project managers can use. Our goal was to review the 16 papers the Purdue team produced on amphibians and establish a single reference value for each PFAS compound we examined, including PFOS, PFOA, PFHxS, and 6:2FTS.

In the paper, we established chronic no-observed-effect concentrations and lowest-observed-effect concentrations that would be valuable for site assessments. For instance, if a PFAS spill occurred at an airport containing high levels of PFOS, these reference values would help project managers determine whether the PFOS levels pose a potential risk to amphibians in the surrounding area.

Why the focus on amphibians?

Jason Conder
Amphibians are thought to be very sensitive to environmental chemicals, like the canary in the coal mine. If something's wrong with the frogs or tadpoles, that’s a warning sign that the contaminant might cause bigger problems. And that’s important for environmental agencies like the EPA and state regulators who enforce policies like the Clean Water Act and CERCLA and investigate sites where PFAS might have been used.

The data and criteria Zach developed in this report will make those evaluations easier. We can take water samples from ponds or streams and compare them to these guidelines to make more informed decisions. If the levels are below the guidelines, we can be confident that there’s no risk to amphibians. If the guidelines are exceeded, we may need to investigate more and conduct testing to see if there are real effects. And if there are effects, we’ll need to figure out how to address them. Like, do we need to do remediation to clean up the site?

And it’s not just important for the military. Airports and other facilities have used aqueous film-forming foam, which contains a lot of PFAS. This foam was often released directly to areas surrounding the facilities, including ponds, wetlands, streams, and aquatic habitat that may be home to frogs, fish, and other critters we care about.

How does PFAS affect amphibians?

Zach Pandelides
As ecological risk assessors, we focus on apical endpoints that can cause a population-level effect, such as survival, growth, and reproduction. If you can affect any of those three, you can affect the ability of a population to be successful in the long term.

Among those, the most sensitive endpoint we could find that had a clear and biologically meaningful effect from PFAS was for growth, which was evaluated by measuring the weights of amphibians in the experiments. Interestingly, we didn't find any effect of PFHxS and 6.2FTS on amphibians, even at high, thousand-microgram-per-liter levels. However, we did find amphibians might be one of the more sensitive species to PFOA.

Amphibian chronic no-effect (NOEC) and low-effect (LOEC) screening levels for PFAS in water.
Table 1. Recommended amphibian chronic no-effect (NOEC) and low-effect (LOEC) screening levels for PFAS in water. (A Critical Review Amphibian PFAS Ecotoxicity Research Studies: Identification of Screening Levels in Water and Other Useful Resources for Site-specific Ecological Risk Assessments- Pandelides, Conder, Choi, Allmon, Hoskins, Lee, Hoverman, Sepúlveda; aGeosyntec Consultants, Purdue University, Department of Forestry and Natural Resources, Purdue University, Department of Agronomy, Purdue University, Department of Environmental Engineering)

What part of the results did you find the most interesting or surprising?

Zach Pandelides
Probably the natural variability in the animals. In my background, I'm used to working with high-throughput model organisms. I did my postdoc in the School of Pharmacy at the University of Mississippi, and I worked in a zebrafish lab. Zebrafish are like a well-oiled machine of a model species.

But working with amphibians is very different. They are not a typical model organism. The researchers can often only collect animals once a year in the spring, so they are more limited in what they can do and how many animals they have available. Also, because they're not in a traditional lab model (they're pulling these animals directly from the outdoors) there's a lot more variation in the biology of these animals, which can make the data a bit messier and more difficult to work with. This variability is really important to be aware of.

Jason Conder
I was surprised that zebrafish, which we routinely work with, are more sensitive to PFOS than amphibians. The threshold for PFOS effects in zebrafish is lower, falling to around the 100-micrograms-per-liter range, compared to the higher threshold observed in amphibians.

But what we saw was that the threshold for toxicity and amphibians didn't really start causing problems until concentrations in water reach over 1000 micrograms per liter. This indicates that amphibians are generally less sensitive to PFOS, which was surprising to me because the assumption is usually that amphibians are among the most sensitive aquatic species. But in this case, they weren't.

Conversely, the data do indicate that amphibians are sensitive for PFOA compared with fish. So, it's an interesting kind of mixed bag for the default assumption that amphibians are more sensitive than other species.

Zach Pandelides
And another thing that I thought was kind of neat was that we didn't really see a strong correlation between the bioconcentration factors (BCF) and the toxicity. We saw a really high BCF for PFOS, but they weren't very sensitive to it. And then the PFOA BCF was lower, an order of magnitude lower, and they were sensitive to that. That was kind of unexpected as well.

What do you hope people take away from this paper?

Zach Pandelides
That's a good question. We saw that a high tissue concentration of PFOS is not toxic to these amphibians, but a lower tissue concentration, relatively speaking, of PFOA, can be toxic. That might not be common to all animals, but that's what we are seeing in frogs. And PFOA can be present in higher concentrations at sites than PFOS.

And so, based on this data, again depending on the concentrations there, some of these PFOA sites may be more of a risk to amphibians than other sites. Knowing this help us make decisions in terms of investigations and cleanups in sites where PFAS is found.

Jason Conder
Often, people assume the worst-case scenario, thinking that any detection of a chemical could cause problems in the environment. Analytical chemists are excellent at detecting extremely low levels of chemicals, including PFAS in water and soil. However, a fundamental premise of toxicology is that the “dose makes the poison.” So you really need to understand that threshold dose. This paper allows us to identify specific thresholds and make informed decisions rather than relying on guesswork.

More Information

Read Zach and Jason's paper from Environmental Toxicology and Chemistry, "A Critical Review of Amphibian Per‐ and Polyfluoroalkyl Substance Ecotoxicity Research Studies: Identification of Screening Levels in Water and Other Useful Resources for Site‐Specific Ecological Risk Assessments."

For consultation on PFAS, contact Jason at This email address is being protected from spambots. You need JavaScript enabled to view it..

Listen to Jason describe human health concerns with PFAS: PFAS: Human Health Concerns | Jason Conder, Ph.D. - YouTube

Learn more about Geosyntec’s PFAS services: Per- and Polyfluoroalkyl Substances (PFAS) (