New ‘magnet’ pulls pesky nonstick pollutants from drinking water | Science News for Students

New ‘magnet’ pulls pesky nonstick pollutants from drinking water

It targets toxic chemicals, which can themselves stick around in the environment — potentially forever
Jul 18, 2017 — 7:10 am EST
frying egg

Many old-style nonstick frying pans relied on coatings containing PFOA or related perfluorinated compounds. Although there has been a move to alternative coatings, these perfluorinated pollutants live on in the environment. And that is driving new research aimed at removing them.

loongar/iStockphoto

Many old-style nonstick frying pans relied on coatings containing PFOA or related perfluorinated compounds. Although there has been a move to alternative coatings, these perfluorinated pollutants live on in the environment. And that is driving new research aimed at removing them.

loongar/iStockphoto

Making the chemical used in many nonstick frying pans, stain-resistant carpets and fire-fighting foams can pollute drinking water. Known as PFOA, this chemical can persist unchanged in the environment for years — perhaps for centuries or longer. And that can be troubling because studies have suggested that PFOA can harm the health of people and animals. But a new lab-made chemical can now remove PFOA from water.

fire-fighting foam
Many fire-fighting foams contain PFCs that pollute the environment, including drinking-water sources. But a new, reusable material can pull at least one of these nasty chemicals out of water.
Dushlik/iStockphoto

Chemicals already existed to filter out PFOA. None, however, work as well as the new one appears to. William Dichtel is a chemist at Northwestern University in Evanston, Ill. He and his colleagues described their new PFOA “magnet” June 14 in the Journal of the American Chemical Society

PFOA is short for perfluorooctanoic (Per-FLUOR-oh-OCK-teh-NO-ik) acid. It’s one of a family of related perfluorinated (Per-FLUOR-ih-NAY-ted) compounds, or PFCs, that toxicologists worry about. Each PFC has a backbone of carbon atoms to which a large number of fluorine atoms are strongly bound. Those fluorines make the chemicals stable. They are so stable, in fact, that some of these chemicals never want to break down.

Because of how long PFOA and some of its chemical cousins can pollute the environment, many companies have cut back on their use. But that hasn’t ended the problem. PFCs released even long ago still sit around, waiting to be picked up by plants and animals.

Already, low levels in all of us

“These compounds are very possibly some of the most persistent organic chemicals we've made to date,” says Christopher Higgins. He’s an environmental engineer at the Colorado School of Mines in Golden. Higgins wasn’t part of this new study. He has, however, been studying the problem of PFC pollution. In the natural environment, he says, these chemicals take practically forever to disappear.

And that’s a concern because the use of these chemicals has been so widespread. They now can be found nearly everywhere. For instance, studies found traces of PFOA and related PFCs in 98 percent of all Americans tested.

In rats and mice, exposure to PFOA raises the risk of certain tumors. But it’s unclear whether it also raises cancer risks in people. Studies in humans have linked the chemical to thyroid disease, to a weakened immune system and to problems for developing fetuses. There are even data linking PFOA and related PFCs to impaired vaccine effectiveness in kids.

PFOA will build up in a person’s body over time. So the U.S. Environmental Protection Agency advises keeping exposures very low — to just 0.07 parts per billion in drinking water. But water in many U.S. towns and cities have far higher levels, recent studies have shown.

Notes Dichtel: “We're finding negative health effects from being exposed to [PFCs] even when they're in trace concentrations.” As such, he says, “It's becoming clear that we need to remove them almost completely.”

Designing a better PFC ‘magnet’

A common way to remove PFOA from water is with a filter that contains a material that acts like a PFC magnet. It will gather molecules of the pollutant onto the material’s surface. This makes the pollutant easy to remove.

Activated carbon is often used this way. But PFOA molecules are only somewhat attracted to it. This allows some PFOA molecules to remain in the water, Dichtel explains.

So his group designed a material to actually target PFCs. This material is a type of polymer. Such molecules are made of chains of repeating chemical units. The new polymer contains repeating units of two different molecules. One is a giant, ring-shaped molecule derived from cornstarch. It’s called beta-cyclodextrin (BAY-tuh SY-klo-DEX-trin). The other is a fluorine-rich molecule called DFB. (That’s short for decafluorobiphenyl.) Its fluorines help the polymer grab onto PFOA, Dichtel says.

Activated carbon grabs any contaminants that are nearby. The new polymer instead selectively attracts those hard-to-get fluorine-rich pollutants, says Karen Wooley. She’s a chemist at Texas A&M University in College Station and was not part of the study.

PFOA chemical structure
PFOA is one of the persistent compounds that can show up throughout the environment. Its chemical structure, here, starts with a chain of linked carbon atoms to which manufacturers have attached atoms of fluorine (F). PFOA’s has a carbon atom at the center of each “X” in this structure.
Edgar181

In tests, the new polymer grabbed 95 percent of PFOA from water. Activated carbon removed only a little more than half of it. Moreover, some common chemicals in water can make activated carbon less effective. But the polymer kept working even when those other chemicals were around.

Best of all, the new polymer is reusable. Washing it with methanol, a type of alcohol, removed the PFOA. This left the polymer ready to pull out more of the pollution.

Dichtel and his colleagues now are working to turn this polymer and others like it into products people can buy. Such materials might one day help homeowners and businesses filter their water.

Higgins at the Colorado School of Mines notes that other PFC pollutants also pose risks. He’s part of a group including Chinese researchers that has been focusing on how to clean up drinking water supplies that are polluted with PFC-based firefighting foams. They found PFOA and nearly 30 other PFCs in affected waters. Scientists only recently discovered nearly half of the PFCs they turned up.

Unlike Dichtel’s group, Higgins’ team found that activated carbon did a decent job of removing PFOA. But activated carbon did not work nearly as well for those other, under-the-radar molecules. Yet they might pose similar environmental and health risks.

His team reported its new findings June 6 in Environmental Science and Technology.

Concludes Higgens, when it comes to getting PFOA and its relatives out of drinking water, “we need all the help we can get.” And new filters could tackle that. This research, he says, “is an effort to do something quite new.”

Power Words

(for more about Power Words, click here)

atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

bond    (v. bound) A semi-permanent attachment between atoms — or groups of atoms — in a molecule. It’s formed by an attractive force between the participating atoms. Once bonded, the atoms will work as a unit. To separate the component atoms, energy must be supplied to the molecule as heat or some other type of radiation.

cancer     Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O.

colleague     Someone who works with another; a co-worker or team member.

compound     (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.

concentration     (in chemistry) A measurement of how much of one substance has been dissolved into another.

contaminant     Pollutant; a chemical, biological or other substance that is unwanted or unnatural in an environment (such as water, soil, air, the body or food).

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity.

environmental engineer     A person who uses science to study and improve the natural environment.

Environmental Protection Agency (or EPA)    A national government agency charged with helping create a cleaner, safer and healthier environment in the United States. Created on Dec. 2, 1970, it reviews data on the possible toxicity of new chemicals (other than foods or drugs, which are regulated by other agencies) before they are approved for sale and use. Where such chemicals may be toxic, it sets limits or guidelines on how much of them may be released into (or allowed to build up in) the air, water or soil.

environmental science     The study of ecosystems to help identify environmental problems and possible solutions. Environmental science can bring together many fields including physics, chemistry, biology and oceanography to understand how ecosystems function and how humans can coexist with them in harmony. People who work in this field are known as environmental scientists.

filter     (in chemistry and environmental science) A device or system that allows some materials to pass through but not others, based on their size or some other feature.

fluorine    An element first discovered in 1886 by Henri Moissan. It takes its name from the Latin word meaning “to flow.” Very reactive, chemically, this element had little commercial use until World War II, when it was used to help make a nuclear-reactor fuel. Later, it was used as ingredients (fluorocarbons) in refrigerants and aerosol propellants. Most recently, it has found widespread use to make nonstick coatings for frying pans, plumbers’ tape, and waterproof clothing.

immune system     The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

methanol     A colorless, toxic, flammable alcohol, sometimes referred to as wood alcohol or methyl alcohol. Each molecule of it contains one carbon atom, four hydrogen atoms and an oxygen atom. It is often used to dissolve things or as a fuel.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

organic     (in chemistry) An adjective that indicates something is carbon-containing; a term that relates to the chemicals that make up living organisms.

perfluorinated chemicals (PFCs)    A family of chemically related compounds used to make products resist stains, oils and water. Among the best-known are PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate). These have been used in “nonstick” cookware, stain-resistant carpeting, food packaging and waterproof clothes. Some are even used in fire-fighting chemicals (such as foams). All are based on molecules with a carbon backbone to which fluorine atoms are bound. These potentially toxic compounds are remarkably stable. That helps them resist breakdown, which allows them to persist for years (potentially centuries) in the environment.

persistent     An adjective for something that is long-lasting.

perfluorooctanoic acid (or PFOA)    One of a host of synthetic, fluorine-rich molecules designed to keep water, oils and other materials from sticking to something. It is one of the most heavily studied members of a large family of very persistent, fluorine-rich compounds used as a nonstick coating and fabric treatment (to repel water and stains). Data in animals suggest that ingestion or inhalation of this compound could cause harm. Sometimes known as C8, this abbreviation denotes the number of carbon atoms making up the molecule's backbone (and to which fluorine atoms are bound).

pollutant     A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

polymer     A substance made from long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself.

thyroid     A gland in the neck that releases hormones, which play a pivotal role in directing development and metabolism (the use of food as fuel).

toxicologist     A scientist who investigates the potential harm posed by physical agents in the environment. These may include materials to which we may be intentionally exposed, such as chemicals, cigarette smoke and foods, or materials to which we are exposed without choice, such as air and water pollutants. Toxicologists may study the risks such exposures cause, how they produce harm or how they move throughout the environment.

tumor     A mass of cells characterized by atypical and often uncontrolled growth. Benign tumors will not spread; they just grow and cause problems if they press against or tighten around healthy tissue. Malignant tumors will ultimately shed cells that can seed the body with new tumors. Malignant tumors are also known as cancers.

Citation

JOURNAL: L. Xiao et al. β-cyclodextrin polymer network sequesters perfluorooctanoic acid at environmentally relevant concentrations. Journal of the American Chemical Society. Vol. 139, June 14, 2017, p. 7689. doi: 10.1021/jacs.7b02381.

JOURNAL: X. Xiao et al. Sorption of poly- and perfluoroalkyl substances (PFASs) relevant to aqueous film-forming foam (AFFF)-impacted groundwater by biochars and activated carbon. Environmental Science and Technology. Vol. 51, June 6, 2017, p. 6342. doi: 10.1021/acs.est.7b00970.

JOURNAL: X. C. Hu et al. Detection of poly- and perfluoroalkyl substances (PFASs) in U.S. drinking water linked to industrial sites, military fire training areas, and wastewater treatment plants. Environmental Science and Technology Letters. Vol. 3, October 11, 2016, p. 344. doi: 10.1021/acs.estlett.6b00260.

JOURNAL: A.M. Calafat et al. Polyfluoroalkyl chemicals in the U.S. population: Data from the National Health and Nutrition Examination Survey (NHANES) 2003–2004 and comparisons with NHANES 1999–2000. Environmental Health Perspectives. Vol. 115, November 2007, p. 1596. doi:

WEBSITE: U.S. Environmental Protection Agency. Basic information about per- and polyfluoroalkyl substances (PFASs): Includes Information on Perfluorooctanoic Acid (PFOA), Perfluorooctyl Sulfonate (PFOS), and All Other PFASs, and on PFCs.

WEBSITE: National Institute of Environmental Health Sciences. Perfluorinated Chemicals (PFCs) homepage.