Long and Short-Chain

By Robert O'Neal. A 9-part series on the old long-chain PFAS like PFOA and PFOS, the newer short-chain PFAS that replaced them, and why both are a problem for water, crops, livestock and people.

Part 1 of 9: The PFAS family

PFAS is not one chemical. It's a family of thousands. They are built on a chain of carbon atoms locked to fluorine, one of the strongest bonds in chemistry. That's why they don't break down.

Scientists sort them by how long that chain is. Long-chain PFAS were the old ones. Short-chain PFAS are mostly the newer replacements.

The ones that show up most in testing:

• PFOA, also called C8. DuPont's Teflon chemical. Long chain.
• PFOS. 3M's chemical for the old Scotchgard and firefighting foam. Long chain.
• PFHxS and PFNA. Often found right alongside PFOS and PFOA.
• GenX. The replacement for PFOA. Shorter chain.
• PFBS. The replacement for PFOS. Short chain.

There are also the fabric treatments that make cloth, carpet and paper resist water, grease and stains. Textile mills used them. Over time some of them break down into chemicals like PFOA.

The next two parts are about the old long-chain PFAS. After that, the replacements, and why swapping one PFAS for another did not fix the problem.

Part 2 of 9: Long-chain PFAS in people

The old long-chain PFAS, mainly PFOA and PFOS, are the most studied. They are also the ones that build up in us.

Once they are in your blood, they stay a long time. It takes about 3 and a half years for half the PFOA to leave your body, and close to 5 years for PFOS. Every new dose stacks on top of the old.

Here is what the research has found.

Cancer. In 2023 the World Health Organization's cancer agency classified PFOA as a cause of cancer in humans, its highest level. It rated PFOS as a possible cause. EPA has called both likely to cause cancer.

Six diseases. The C8 Science Panel studied nearly 70,000 people near DuPont's West Virginia plant. It found probable links between PFOA and kidney cancer, testicular cancer, thyroid disease, ulcerative colitis, high cholesterol, and high blood pressure in pregnancy.

Immune system. Studies in children and adults have tied PFOA and PFOS to weaker responses to vaccines and more infections.

The C8 numbers came from people who drank contaminated water for years. That is the same way most of us take them in, through water and food.

Part 3 of 9: Long-chain PFAS on the farm

Long-chain PFAS stick to soil. On land where sludge was spread, they can stay in the top layer for decades. Once they are in the soil, they are very hard to get out.

They don't move up into plants as easily as the short-chain ones. But some still gets into grass and hay. Cattle graze that grass and eat that hay all day, every day, for years.

PFOS is the one that builds up in livestock. It shows up in blood, liver, kidneys, milk and meat.

Maine found this out the hard way. In 2016 a dairy farm was found with high PFAS in its soil, water, hay and milk. The source was sludge spread on the fields years before. Two more dairies were found in 2020 through store milk testing. The first farm had to shut down.

Maine now has action levels for PFOS in milk and beef. If a farm's milk or beef is over the limit, it can't be sold.

In Michigan, beef from a family cattle farm was pulled from the market after testing found PFOS. The cattle ate feed crops grown on fields fertilized with sludge.

There is some good news. Once animals stop taking it in, the levels in their blood, meat and milk go down over time.

But the soil stays the same. That's why knowing what's in your ground matters.

Part 4 of 9: Why they switched

By 2000 the old PFAS were in trouble. They were turning up in people's blood all over the world.

In 2000, 3M announced it would stop making PFOS. In 2006 the EPA got DuPont, 3M and six other companies to agree to phase out PFOA by 2015.

The companies did not stop using PFAS. They switched to shorter versions. GenX replaced PFOA. PFBS replaced PFOS.

The selling point was that the shorter ones leave the body faster.

How long it takes for half of each to leave a person's blood:

• PFOS: about 5 years
• PFOA: about 3½ years
• PFBS: about 26 days

That sounds like a big improvement. The next parts show why it is not the whole story.

Part 5 of 9: Faster through water, harder to filter

Short-chain PFAS dissolve in water more easily than the old ones. That changes how they behave once they get out.

They move farther and faster through groundwater, creeks and rivers. A spill or a field of sludge can spread them over a wider area.

They are also harder to get out of water.

The most common way to clean PFAS out of water is activated carbon. It works well on the long-chain ones like PFOA and PFOS. On the short-chain ones it works much worse. In tests, short-chain PFAS break through carbon filters much sooner, and some barely get caught at all.

That matters for town water plants. It also matters for anyone on a well with a carbon filter under the sink. Ask what your filter is rated to remove. Reverse osmosis and certain resins do better on short-chain PFAS.

They still don't break down. Once they are in the water, they stay.

Part 6 of 9: Crops take them up more

This is the part that matters most to farmers.

Because short-chain PFAS dissolve in water, plants pull them up through their roots along with the water. The long-chain ones mostly stick to the soil or stay in the roots. The short-chain ones travel up into the leaves and fruit, the parts we eat.

Researchers at the Colorado School of Mines grew lettuce, tomatoes, peas, radishes and celery in soil treated with biosolids. The short-chain PFAS showed up in the crops at much higher levels than the long-chain ones. Field-grown lettuce and tomatoes showed the same thing.

A University of Maine study found one short-chain PFAS, PFBA, highest by far in tomato fruit, then in tall fescue and lettuce.

Leafy greens tend to pick up the most. Grains and peeled potatoes pick up the least.

Testing on a farm right here in Society Hill found the same pattern. See Who's Checking Our Food, Part 4.

Grass and hay take it up too. Michigan State researchers note that short-chain PFAS build up most in leaves. Cattle eat the leaves. Then it can show up in milk and meat.

On land treated with sludge, the old PFAS tend to stay in the soil. The new ones are the ones more likely to end up on the plate.

Part 7 of 9: What about tobacco?

Tobacco is still grown here in the Pee Dee. So the question comes up: what about tobacco grown on land that got sludge?

The honest answer is nobody has studied it. We could not find a single study that grew tobacco on PFAS-contaminated soil and tested the leaf.

Here's why it's worth asking. Tobacco is a leaf crop. As the last part showed, the short-chain PFAS travel up the plant and build up in the leaves. That's what happens in lettuce and in grass and hay. There's no reason to think tobacco works differently. But that's an educated guess, not a test result.

The one study we found was run by Philip Morris on its own store-bought products. It checked for 51 PFAS. Only one short-chain PFAS showed up, at low levels like those found in a lot of plant foods, and it wasn't found in the smoke. But that tobacco wasn't grown on known contaminated land, and it was the company testing its own product.

What nobody knows yet: how much PFAS from contaminated leaf reaches someone who smokes or chews it, and what burning does to it.

If you grow tobacco on ground that got sludge, the only way to know is to test the cured leaf. Ask the lab to include the short-chain ones like PFBA.

Part 8 of 9: What the health studies show

Short-chain PFAS leave the body faster. But if you keep drinking the water or eating the food, they keep coming in. Your level stays up.

Here is what EPA found when it looked at the two main replacements.

GenX. In 2021 EPA finished its review. In animal studies, GenX caused problems in the liver, kidneys, immune system and the development of offspring. EPA also noted liver and pancreatic tumors. The liver was the most sensitive.

EPA set the safe daily amount for GenX about 26 times lower than its 2018 draft. That made it stricter than the safe amount EPA had set for PFOA back in 2016.

PFBS. EPA's 2021 review found effects on the thyroid, kidneys, and reproduction and development in animals. EPA rates PFBS as less toxic than GenX, PFOA and PFOS. Less toxic is not the same as safe.

Chemours, which makes GenX, has said it is much less hazardous than the chemical it replaced. EPA's own review found it more harmful than first thought.

Part 9 of 9: A regrettable substitution

Scientists have a name for swapping a harmful chemical for a close cousin that turns out to be a problem too. They call it a regrettable substitution.

That is what happened here.

The companies had decades of studies on PFOA and PFOS. The replacements have far fewer. Massachusetts science advisors noted that the long-chain ones have been studied in much more depth than the short-chain ones. People were exposed before anyone knew the full risks.

Here is the trade that was made:

• The old PFAS build up in people for years.
• The new ones leave people faster, but spread farther in water, slip past common filters, and get pulled up into crops more.
• Both kinds never break down.

Many scientists now say PFAS should be handled as one class instead of one chemical at a time. Otherwise the industry can keep swapping one for the next.

For those of us on farms and wells, it means testing for more than PFOA and PFOS. Ask the lab to include the short-chain ones like PFBS, PFBA and GenX.