A recent investigation has evaluated how toxic various types of per- and polyfluoroalkyl substances (PFAS), often referred to as “forever chemicals,” become when they combine in the environment and the human body.
A groundbreaking study has assessed the toxicity levels of several forms of per- and polyfluoroalkyl substances (PFAS), commonly known as “forever chemicals,” when they are mixed in the environment and within our bodies.
The encouraging result is that the individual levels of cytotoxicity and neurotoxicity for most of the tested chemicals were found to be fairly low.
However, the concerning discovery is that when these chemicals came together, they turned the entire mixture toxic.
“Although these chemicals share similar structures, their effects are not equal—some are more toxic than others. When combined, all components add to the mixture’s overall cytotoxicity and neurotoxicity,” explains the study’s lead author, Karla RÃos-Bonilla, a chemistry PhD candidate at the University at Buffalo.
“In the laboratory tests applied in this study, most types of PFAS we analyzed did not show significant toxicity on their own. Yet, analyzing a sample containing multiple PFAS reveals the toxicity present,” adds co-author Diana Aga, PhD, director of the RENEW Institute and a distinguished professor at the UB Department of Chemistry.
This research was carried out in partnership with Beate Escher from the Helmholtz Centre for Environmental Research (UFZ) in Leipzig, Germany, where RÃos-Bonilla conducted the in vitro toxicity tests in the CITEPro high-throughput screening facility. The findings were published on September 11 in the journal Environmental Science and Technology, which is affiliated with the American Chemical Society.
This study is unique as it evaluates the mixture toxicity of PFAS. These synthetic chemicals have been in consumer products such as nonstick cookware and cosmetics for several decades and are known to persist in the environment for hundreds to thousands of years. Currently, they are found in at least 45% of America’s drinking water and in the bloodstream of nearly all Americans, with associations made to cancer and neurodevelopmental disorders.
Earlier this year, the U.S. Environmental Protection Agency (EPA) established its first-ever drinking water standards for six specific types of PFAS. Despite this, there are believed to be over 15,000 different variants present in the environment, with only a few currently regulated.
“We can regulate six types of PFAS because we have sufficient knowledge about their toxicity. Unfortunately, we cannot impose regulations on other PFAS until we understand their toxic effects,” Aga states, who is also the principal investigator for the EPA STAR grant that supported this research. “We need to set limits on contamination for each PFAS that reflects their toxicity. Knowing how potent they are relative to one another in mixtures is crucial for regulation, alongside their expected environmental concentrations.”
Other contributors from UB include G. Ekin Atilla-Gokcumen, PhD, Dr. Marjorie E. Winkler Distinguished Professor and associate chair in the Department of Chemistry, and Judith Cristobal, PhD, a senior research scientist.
RÃos-Bonilla is receiving additional support through a graduate fellowship from the National Institute of Environmental Health Sciences (NIEHS) under the National Institutes of Health (NIH).
PFOA and PFOS play significant roles in mixture toxicity
For the study, the researchers formulated their own PFAS mixtures to represent the average concentration in American blood serum and surface water samples identified in the U.S. RÃos-Bonilla utilized data from the U.S. Centers for Disease Control and Prevention and the U.S. Geological Survey to establish the typical concentration ratios of PFAS present in human blood and surface water.
These mixtures were then assessed for their impact on two types of cell lines: one to evaluate mitochondrial toxicity and oxidative stress and the other for neurotoxicity.
Among the 12 PFAS included in the water mixture, perfluorooctanoic acid (PFOA)—widely used in nonstick pans and firefighting foam—turned out to be the most cytotoxic contributor, accounting for up to 42% of the total cytotoxicity of the mixture.
Meanwhile, both PFOA and perfluorooctane sulfonic acid (PFOS) contributed roughly equally (25%) to the neurotoxicity test, despite their individual concentrations being only 10% and 15% of the mixture, respectively.
In the blood mixture containing four PFAS, PFOA again emerged as the leading cytotoxic agent for both cell lines. Even with its molar contribution being just 29%, PFOA induced 68% of the cytotoxicity in the cytotoxicity test and 38% in the neurotoxicity test.
Interestingly, toxicity levels were found to be very high when analyzing extracts from actual biosolid samples obtained from a municipal wastewater treatment facility, even though the commonly measured concentrations of PFOA and other PFAS in these samples were low.
“This indicates that there are many other PFAS and unidentified chemicals present in the biosolids, which significantly contribute to the observed toxicity,” notes Aga.
Synergistic effects versus additive effects
One of the objectives of the researchers was to investigate whether PFAS compounds exhibit synergistic effects, where their combined toxicity exceeds the expected sum of their individual effects. However, their findings suggested that the effects of PFAS were concentration-additive, implying that existing toxic mixture prediction models could effectively forecast the combined effects of mixtures.
“With up to 12 PFAS showing concentration-additive behavior in terms of cytotoxicity and specific neurotoxicity, it is likely that the thousands of PFAS currently in usage are behaving similarly,” remarks Escher. “Mixtures present a greater risk than individual PFAS. As they occur in combination, they should be regulated accordingly.”
The study’s authors believe that their findings will significantly aid in evaluating the effectiveness of remediation strategies. While attempting to break down PFAS, harmful byproducts can arise that might evade detection through standard chemical analysis. Therefore, evaluating the toxicity of a sample post-treatment might be the sole method to determine the success of a remediation technique.
“Toxicity tests can act as a supportive measure when standard analytical chemistry does not provide a complete picture, especially in contaminated sites where the identities of harmful substances remain unidentified,” emphasizes Aga.
