Mixtures of different types of PFAS compounds are often more toxic than single chemicals, first-of-its-kind research finds, suggesting humans’ exposure to the chemicals is more dangerous than previously thought.
Humans are almost always exposed to more than one PFAS compound at a time, but regulatory agencies largely look at the chemicals in isolation from one another, meaning regulators are probably underestimating the health threat.
“Our point is that PFAS needs to be regulated as mixtures,” said Diana Aga, a study co-author with the University of Buffalo, which partnered with the Helmholtz Centre for Environmental Research in Germany.
PFAS are a class of about 15,000 compounds most frequently used to make products water-, stain- and grease-resistant. They have been linked to cancer, birth defects, decreased immunity, high cholesterol, kidney disease and a range of other serious health problems. They are dubbed “forever chemicals” because they do not naturally break down in the environment.
The study, which relied on modeling with in vitro cells, not human or animal studies, checked the neurotoxicity and cytotoxicity for combinations of up to 12 PFAS compounds that the federal government has regularly found in water. It also looked at a combination of four PFAS that the US Centers for Disease Control and Prevention has often found in blood serum.
Cytotoxicity refers to toxicity to cells, and the researchers measured oxidative stress, which is a marker of potential health impacts.
The research did not find a synergistic effect in which a combination of PFAS enhanced the chemicals’ toxicity – instead, it showed that the toxicity is additive.
Aga likened it to finding that “one plus one equals two”, rather than “one plus one equals 10”, as some had feared might be the case with PFAS compounds.
“Originally, that’s what we thought, but it’s not synergistic. It’s just simple addition,” Aga said.
Still, it is a problem in the real world because some compounds are more toxic than others. PFOA and PFOS are two of the most common and dangerous PFAS chemicals, research over recent decades has found, and one of those compounds is very frequently found in contaminated human blood or drinking water.
The sum of those chemicals can present a danger, even if they are below the Environmental Protection Agency’s drinking-water limits of 4ppt (parts per trillion) for each.
Hypothetically, if PFOA and PFOS levels were present at 3ppt each, then the water would be considered safe by EPA standards. But the sum of each chemical’s toxicity would probably make the water dangerously toxic.
The new study found PFOA to be the most cytotoxic, making up to 42% of the water mixture’s cytotoxicity. In the blood sample, it accounted for nearly 70% of the cytotoxicity, and 38% of the neurotoxicity.
The study also looked at PFAS combinations found in sewage sludge used as fertilizer and spread on cropland as a cheap fertilizer. Sewage sludge, or biosolids, is a byproduct of the water-treatment process that is left over when water is separated from human and industrial waste discharged into the nation’s sewer systems. It can contain any of tens of thousands of chemicals sent into the US sewer system.
Environmental groups have blasted the practice and sued the EPA for allowing it because biosolids can pollute water and contaminate food.
When researchers analyzed the toxicity of biosolid samples collected from a municipal wastewater treatment plant, they found very high toxicities despite low concentrations of PFOA and other PFAS in the sample.
“It was more toxic than what we predicted, not necessarily because of other PFAS, but other chemicals in biosolids that can cause toxicity,” Aga said.
