'Forever chemicals' are everywhere: Most of their health effects are unknown

The worms' soupy meal is laced with a hidden ingredient, invisible so-called "forever chemicals" found in America's drinking water, our food and farmlands, even lurking in our bodies.

It's a chemical safety test, said Duke postdoctoral fellow Tess Leuthner. The worms are C. elegans, a garden- and compost-dwelling nematode that is helping researchers such as Baugh and Leuthner uncover new insights into the health effects of human-made chemicals used in everyday products ranging from cookware to candy wrappers.

The work revolves around per- and polyfluoroalkyl substances, or PFAS, a group of long-lasting compounds that have been used in industry and consumer goods since the 1940s because of their ability to resist grease, oil, water and heat.

Virtually Everywhere

PFAS are almost impossible to avoid. The chemicals are used to keep food from sticking to our pots and pans; make outdoor gear water-resistant; protect our furniture and textiles from stains, among many other uses. They're in our takeout containers, rain gear, carpets, paint, even dental floss and makeup.

The substances are called "forever chemicals" because of their longevity. PFAS consist of chains of carbon and fluorine atoms linked together. It's one of the strongest chemical bonds known.

"It's these strong carbon-fluorine bonds that make PFAS so durable but also make them impossible to degrade," Leuthner said.

That's why, once they're produced they tend to stick around. They build up and essentially never break down.

"Any PFAS that's already in the environment is there to stay," Leuthner said.

That's what happened in North Carolina's Cape Fear River, where chemicals discharged into the waterway by a chemical manufacturing plant have left downstream communities struggling with tainted drinking water for decades.

That's also what befell service members and residents living near North Carolina's Fort Bragg and hundreds of other military sites across the country, where PFAS from firefighting foam has made its way into the groundwater, contaminating private wells used by nearby residents.

Today, nearly all people in the U.S. have PFAS in their blood. Their use is so widespread that PFAS have even turned up in polar bears and the middle of the open ocean.

These chemicals exist in more than 14,000 forms. While several have been linked to health problems, such as cancer, lower birthweight and liver damage, the vast majority have never been tested. The potential health effects from exposure are unknown.

And while some PFAS are no longer manufactured in the U.S., they are still found in older or imported goods, and newer replacement chemicals continue to take their place.

So what do we do? Duke researchers say there may be a way to help close the knowledge gap -- using tiny transparent worms.

Toxicity Isn't One-Size-Fits-All

In a recent study, a Duke team led by Leuthner, Baugh and Heather Stapleton of Duke's Nicholas School of the Environment exposed C. elegans worms to different doses of 13 PFAS chemicals -- some old, some newer -- and then measured the effects of the chemicals on their growth.

When they compared the PFAS-treated worms to worms that were not exposed, they found that all of the chemicals they tested stunted the worms' growth. But some PFAS took a toll at much lower doses than others, the researchers found.

The most toxic chemical, PFOSA, was a thousand times more toxic than the least toxic chemical, PFBA.

What's more, not every worm strain responded in the same way. Some strains suffered adverse effects at lower doses of certain chemicals than others, suggesting differences in sensitivity that are rooted in their genes.

"This is the first evidence that genetic variation contributes to susceptibility to PFAS toxicity," Leuthner said.

The health risks to worms might seem like a trivial concern.

But many disease-causing genes in humans have counterparts in C. elegans. And while humans and worms appear very different, they share many of the same metabolic and developmental pathways, Leuthner said.

High-Throughput Testing

What's more, the worms' small size and fast development means researchers can study the effects of diverse chemicals on large numbers of them in a relatively short amount of time.

Traditional toxicity testing in animals such as mice and rabbits can take over a year to complete; whereas similar experiments in C. elegans take less than a week.

The work is part of a larger NIH-funded study aimed at using worm genetics to better predict which chemical exposures are most likely to hurt people's health.

The idea is to pinpoint gene variants that, if counterparts exist in humans, could help identify people who may be more sensitive to some environmental pollutants than others due to their genetic makeup.

"This is really critical, because humans are genetically diverse," Leuthner said.

As a next step, the researchers are working to pin down which genes are responsible for the differences they found.

The work could help identify people or populations who might be particularly susceptible, or help pinpoint untested PFAS with the most potential for harm and flag them for future study.

"This could really speed up testing and regulation," Leuthner said.

This research was funded by the National Institutes of Health (R01ES029930, P42 ES010356 and F32-ES034954) and the Duke Department of Biology.