Mixtures of different types of PFAS compounds are often more toxic than individual chemicals, the first of its kind research findsindicating that human exposure to the chemicals is more dangerous than previously thought.
People are almost always exposed to more than one PFAS compound at a time, but regulators largely look at the chemicals in isolation, meaning regulators are likely underestimating the health threat.
“Our point is that PFAS should be regulated as mixtures,” said Diana Aga, co-author of the study at the University at Buffalo, who worked with the Helmholtz Center for Environmental Research in Germany.
PFAS are a class of approximately 15,000 compounds most commonly used to make products water, stain and grease resistant. They have been linked to cancer, birth defects, reduced immunity, high cholesterol, kidney disease and a range of other serious health problems. They are called ‘forever chemicals’ because they do not break down naturally in the environment.
The study, which relied on in vitro cell modeling and not human or animal studies, monitored neurotoxicity and cytotoxicity for combinations of up to twelve PFAS compounds that the federal government has regularly found in water. It also looked at a combination of four PFAS that the U.S. Centers for Disease Control and Prevention has commonly found in blood serum.
Cytotoxicity refers to toxicity to cells, and the researchers measured oxidative stress, which is a marker of potential health consequences.
The study found no synergistic effect where a combination of PFAS enhanced the toxicity of the chemicals; instead, it showed that the toxicity is additive.
Aga compared it to discovering that “one plus one equals two,” rather than “one plus one equals 10,” as some feared might be the case with PFAS compounds.
“We originally thought so too, but it doesn’t work synergistically. It’s just a simple addition,” Aga said.
Still, it’s a problem in the real world because some compounds are more toxic than others. PFOA and PFOS are two of the most common common and dangerous Research over the past decades has shown that PFAS chemicals are one of those compounds very commonly found in contaminated human blood or drinking water.
The sum of these chemicals can pose a hazard even if they are below the Environmental Protection Agency’s drinking water limits of 4ppt (parts per trillion) each.
Hypothetically, the water would be considered safe by EPA standards if the PFOA and PFOS levels were 3ppt each. But the sum of each chemical’s toxicity would likely make the water dangerously toxic.
The new study found that PFOA is the most cytotoxic, accounting for 42% of the water mixture’s cytotoxicity. In the blood sample, it was responsible for almost 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 remains when water is separated from human and industrial waste that is discharged into the country’s sewage system. It can contain tens of thousands of chemicals that end up in the U.S. sewage system.
Environmental groups have denounced the practice and sued the EPA for allowing it because biowaste can contaminate 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 the low concentrations of PFOA and other PFAS in the sample.
“It was more toxic than we predicted, not necessarily because of other PFAS, but because of other chemicals in biosolids that can cause toxicity,” Aga said.