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Bacteria can't eat, fire can't burn, buried in the ground will only pollute the soil... how to deal with this kind of substance?

In 1938, Roy J. Plunkett, a chemist working in a New Jersey laboratory on refrigerants for refrigerators, stumbled upon a new material called polytetrafluoroethylene. It is resistant to high temperatures, can resist strong acids, strong bases or strong oxidants corrosion, and difficult to dissolve in organic solvents.

During World War II, engineers involved in the Manhattan Project took a fancy to it. PTFE was coated on pipes and valves at uranium enrichment plants to protect them from aggressive attacks by uranium hexafluoride (enriched feed) and played a role in the atomic bomb manufacturing process.

After the war, PTFE had a more peaceful use: from the 1950s onwards, it appeared in ordinary people's lives as a coating for non-stick pans. To avoid polymer caking, factories that produce PTFE products use a surfactant called perfluorooctanoic acid (PFOA) on a large scale.

But as PFOA became more widely used, people gradually realized that this substance was not "peaceful." In the late 1990s, a farmer in West Virginia found that his cows kept dying for unknown reasons. The farmer had sold a plot of land to a nearby DuPont plant for landfill, but he suspected the plant people were using it for more than just "landfill."

DuPont is the company that owns the patent for PTFE, and it turns out that the plant has been discharging hundreds of tons of PFOA into the nearby Ohio River for years. The use of PFOA was not regulated at the time, and the farmer's case against DuPont ended in a settlement, but the incident itself raised concerns and more people began to worry about the health risks of PFOA.

In recent years, PFOA has been associated with kidney cancer, testicular cancer and other diseases. Although PFOA as a processing aid can be removed and may not be detected in the final PTFE product, PFOA discharged into the environment by factories is difficult to decompose and can exist for a long time in the human body, which cannot be ignored.

Today, PFOA has withdrawn from the manufacturing process of non-stick pans and many other products, and most manufacturers of PFOA have stopped production. However, there are thousands of perfluorinated or polyfluoroalkyl substances (PFAS) that are difficult to degrade, such as PFOA, and they are almost everywhere. They are called "permanent chemicals" and are accumulating in our bodies.

How dangerous is it? Perfluorinated or polyfluoroalkyl substances (PFAS) are rich in carbon-fluorine bonds, which are short and strong, and are the main reason why they are difficult to decompose. Therefore, they are often used in the manufacture of goods that require heat, water, oil or stain resistance. Such as sunscreen, food packaging, smart phones... PFAS may be used in the manufacture of a variety of products.

If PFAS causes physical harm, it is likely that workers will bear the brunt. In 2012, Emory University scientists surveyed workers at DuPont plants in West Virginia who were exposed to perfluorooctane (PFOA). Workers exposed to PFOA on a daily basis were found to be about twice as likely to die from mesothelioma and chronic kidney disease than workers at other DuPont plants. Mortality aside, these workers also had a significantly higher risk of kidney cancer and other kidney diseases than other workers.

In addition to workers, factory emissions also affect people and livestock who use water locally. In 2013, a group of researchers interviewed residents of the central Ohio Valley who lived near the plant between 1952 and 2011 and used water contaminated with PFOA. The results showed that people with higher serum PFOA concentrations were also more likely to develop kidney cancer and testicular cancer.

Of course, dangerous perfluoro/polyfluoroalkyl substances are not the only ones. For example, perfluorooctane sulfonate (PFOS) was once a ubiquitous surfactant, used as an antifouling spray for carpets and in fire-fighting foams-many of which overlapped with PFOA. Previous studies have linked PFOS to thyroid disease, chronic kidney disease, and preeclampsia in pregnant women; a new study this month found that people in the top 10 percent of people with PFOS in their blood were 4.5 times more likely to develop hepatocellular carcinoma.

Firefighters (Photo: Unsplash)

In 2021, scientists at Rutgers University found that firefighters had higher levels of nine PFAS in their blood than the general population. PFAS in their bodies may have come from fire-fighting foam and protective clothing. The International Agency for Research on Cancer lists firefighters as a carcinogenic occupation, and although the main cause of cancer in firefighters may be smoke inhalation or exposure to hazardous chemicals in fires, PFAS should not be underestimated. The International Firefighters Association advised firefighters in August to wear fire-fighting gear only when absolutely necessary. Earlier this year, dozens of U.S. firefighters sued manufacturers of protective gear, challenging PFAS for causing their own health problems, some cancer and some other diseases.

Perhaps more people are neither in occupations that require particular exposure to PFAS nor living near chemical plants that emit large amounts of PFAS pollutants. But these "permanent chemicals" have accumulated in the environment for decades, and there may not be many Earthlings without PFAS in their bodies today. Since everyone has it, people are more concerned about the question of more and less.

Can't you drink the rain on the Qinghai-Tibet Plateau? As human awareness of PFAS toxicity continues to refresh, people's tolerance for PFAS is getting lower and lower. Over the past 20 years, the upper limit of safe PFAS concentrations in drinking water, surface water and soil has declined sharply. Take perfluorooctanoic acid (PFOA) as an example:

In 2002, West Virginia issued a safe drinking water PFOA level of 150000 ng/L. In 2016, the U.S. Environmental Protection Agency set an upper limit of 70 ng/L for the total concentration of PFOA and PFOS in drinking water. In June, the EPA issued a new advisory setting the safe concentration of PFOA in life-long drinking water at 0.004 ng/L.

On the one hand, safety standards are becoming stricter and stricter, and on the other hand, PFAS concentrations in the environment are difficult to meet the standards. A paper published in August by scientists at Stockholm University and ETH Zurich collated PFOA levels in rainwater from previous studies in different parts of the world. The data show that the PFOA concentration in rainwater collected from the Qinghai-Tibet Plateau is the lowest, but it is still 0.055 ng/L, which is more than ten times higher than 0.004 ng/L. If the EPA's latest guidelines are followed, there may be no place in the world where rainwater is safe to drink.

Rain (Photo Credit: Unsplash)

In China, a research team from Peking University gave a drinking water recommendation in 2019 based on the relationship between PFOA / PFOS content in drinking water and PFOA / PFOS concentration in human blood: PFOA should not exceed 85 ng/L and PFOS should not exceed 47 ng/L. This is closer to the safety standards provided by the EPA in 2016.

In 2021, a retrospective study published by Tsinghua University research team integrated 526 drinking water sample data from 55 cities in China and found that residents in East China and Southwest China were at high risk of exposure to PFAS. Some of these cities have drinking water PFOA concentrations exceeding 100 ng/L, while drinking water extracted near certain fluorochemical plants has PFOA concentrations exceeding 3000 ng/L.

What else could he do? In any case, it is difficult to prevent these "permanent chemicals" from entering the body. Some scientists tactfully thought that regular donors should have the opportunity to eliminate some PFAS from their blood.

In a study published in April, scientists recruited 285 firefighters in Australia-people who are regularly exposed to PFAS-for a year-long experiment. The researchers randomly divided the firefighters into three groups: one group donated plasma every six weeks (nine times in total), two donated whole blood every 12 weeks (five times in total), and three were a control group that donated nothing.

Photo by Pixabay

The results showed that both whole blood and plasma donation could significantly reduce PFAS levels in serum. At the end of the experiment, serum PFAS levels decreased by 10% in whole blood donors and by 30% in plasma donors. However, there was no significant change in serum PFAS concentration in the control group.

It sounds like a free and easy way to detox, but not everyone is suitable for donating blood. Then, it is still necessary to avoid eating PFAS into the body from the source. It is not enough to filter them out of the water; PFAS will eventually return to the environment without proper degradation protocols.

Since PFAS is referred to as a "permanent chemical," the existing degradation conditions for PFAS are harsh. For example, under extreme temperatures and pressures, they break down, but this is very energy-intensive and expensive. But in August, scientists at Northwestern University and others found a new way to break down PFAS under milder conditions.

When faced with perfluorocarboxylic acids (PFCA), the researchers were not eager to break the strong carbon-fluorine bonds, but instead focused on oxygen-containing groups at one end of the molecule. PFCA is heated in a mixture of dimethyl sulfoxide (DMSO) and water at 120℃. In the presence of sodium hydroxide, PFCA will undergo decarboxylation reaction, just like "decapitation." After that, fluorine atoms will break free from the molecules one by one to form fluorine ions--the safest form of fluorine, scientists say.

The products of the reaction, in addition to inorganic fluorides, are small organic molecules, and the "permanent" pollutants disappear. The scientists published their findings in the journal Science. Of course, this is not the end point. PFCA is only one large class of PFAS (PFOA belongs to this class), and scientists will continue to solve other PFAS classes.

Paper links:

https://pubs.acs.org/doi/10.1021/acs.est.2c02765

https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2790905

https://www.science.org/doi/10.1126/science.abm8868

https://academic.oup.com/aje/article/176/10/909/93256

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3855514/

https://www.jhep-reports.eu/article/S2589-5559(22)00122-7/fulltext

https://enveurope.springeropen.com/articles/10.1186/s12302-020-00425-3

References:

https://www.nytimes.com/2016/01/10/magazine/the-lawyer-who-became-duponts-worst-nightmare.html

https://www.rutgers.edu/news/volunteer-firefighters-have-higher-levels-forever-chemicals

https://www.epa.gov/sdwa/questions-and-answers-drinking-water-health-advisories-pfoa-pfos-genx-chemicals-and-pfbs

https://www.cbsnews.com/news/firefighters-pfas-lawsuit/https://www.cbsnews.com/news/firefighters-pfas-lawsuit/

https://www.nbcnews.com/health/health-news/firefighter-gear-may-contain-chemicals-linked-cancer-rcna44511

This article comes from Weixin Official Accounts: Global Science (ID: huanqiukexue), author: chestnut, revision: clefable

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