Vivian Nguyen/ Stanford University
People have used chemistry to improve their lives for tens of thousands of years. An early example: fire. Our prehistoric ancestors tamed flames to transform plants and animal products — that is, to cook them into food. Over time, their descendants learned about the chemical properties of rocks and other minerals, and of chemicals derived from plants and animals. They mixed materials together. Sometimes, they also applied heat, pressure or both. Through trial and error, they learned how to make new and useful materials. Paints and soap are two notable early examples.
Today, chemistry plays a role in almost every product imaginable. Manufacturing companies have registered more than 83,000 chemicals with the U.S. government. Many of these find use in everything from foods and plastics to trucks and electronics.
Making, using and disposing of these chemicals, however, can pose risks to people or wildlife. Some chemicals, after all, are made from toxic raw materials, such as mercury or lead. Making other chemicals requires huge amounts of energy, clean water or other natural resources. And as we use them or discard them as trash, many chemicals can pollute the air, water or soil.
This high tech skateboard is made from rugged polycarbonate plastic. Yet its building blocks — molecules of bisphenol A — can pose problems once they get into water, foods and more. Fortunately, green chemists are at work on solutions for that and a host of other problems. Their goal: to make consumer products safer and kinder to the environment.
In the early 1990s, chemist Paul Anastas called for a change. While working for the U.S. Environmental Protection Agency, or EPA, he recognized that chemists usually probe possible risks of chemicals long after they have developed them. Anastas urged his fellow chemists instead to design products that would be safer and cleaner from the start.
The color green is often associated with anything that is good for the environment. So Anastas called this new field “green chemistry.” (It’s also sometimes called sustainable chemistry.)
In 1998, Anastas and a fellow chemist, John Warner, published 12 principles of green chemistry. They recommended that chemists cut wastes, reduce the toxicity of the materials they use and produce goods using processes that are safer. They also called for designing new chemicals that will break down harmlessly in the environment.
Today, Terry Collins directs the Institute for Green Science at Carnegie Mellon University in Pittsburgh, Pa. Green chemists work in laboratories, just as other chemists do. However, green chemists share a different goal, Collins explains. “We are working to develop a field of chemistry that can replace polluting technologies, one product or process at a time.”
Peel dirt right off of clothes
Green chemists often start by identifying chemical products or processes that are wasteful, polluting or toxic. Then they find ways to make them kinder to the environment. That might mean changing a process so that it uses less energy. Or it could mean swapping out harmful ingredients for alternatives. Some alternatives might be safer. Others might have the advantage of breaking down in the presence of water or sunlight.
One family of chemicals targeted by green chemists are known as surfactants (Sur-FAK-tuntz). They help mix liquids that would not ordinarily do so. Examples include oil and water. Each surfactant molecule has one end that is hydrophilic (HI-droh-FIL-ik). That means it is attracted to water. The other end is hydrophobic (HI-droh-FO-bik). It repels water.
Surfactants are important ingredients in laundry detergents. They help lift dirt, which usually contains oils, out of clothes. In the United States, nonylphenol ethoxylates (NON-ul-FEE-null Ee-THOX-uh-lates) are a common class of surfactants. Because of their long name, chemists usually just refer to them as NPEs.
After use, NPEs go down the drain. From there, they flow into wastewater-treatment plants. Few such plants can remove NPEs from wastewater. So when they release treated water into lakes and rivers, NPEs will remain part of the mix. Eventually, NPEs will break down to form another chemical called nonylphenol. This chemical is “extremely toxic” to fish and green plants, EPA notes.
Canada and the European Union have banned NPEs in detergents. The United States, however, still uses thousands of tons of these chemicals every year. Not surprisingly, researchers have been finding high levels of nonylphenol in waters across North America.
Ramaswamy Nagarajan is a plastics engineer at the University of Massachusetts in Lowell. He and his students are developing a substitute for NPEs. They started with a green source — apple and orange peels. Microbes in the Gulf of Mexico inspired their choices.
The 2010 Deepwater Horizon oil spill released almost 5 million barrels of crude oil in the Gulf. Afterward, bacteria in the water started breaking down the oil. Nagarajan learned that the microbes had made natural surfactants. These substances contained long chains of linked sugar molecules, called polysaccharides (PAH-lee-SAK-uh-RIDES). So the Lowell research team turned to a natural source of polysaccharides for their new green surfactants.
“We are using pectin,” explains Nagarajan. Fruit peels and many other food wastes contain this edible polysaccharide. In fact, home canners put pectin in their jams and jellies to make them gel. Best of all, Nagarajan notes, “bacteria can break it down.” Natural pectin degrades harmlessly. Eventually, it vanishes from the environment — unlike the persistent and harmful nonylphenol.
To turn pectin into a surfactant, the chemists add a group of atoms to each pectin molecule. The process takes 30 minutes in a special laboratory microwave oven. When it’s done, each pectin molecule now has a hydrophilic, or water-loving, chemical group (a collection of bound atoms) at one of its ends. At the other end: an oil-loving chemical group.
Green chemists still face more work ahead before pectins become widely used surfactants. One problem: their size. As large molecules, pectins do not dissolve well in water. Nagarajan’s team is now working to overcome that. Their surfactant also does not yet remove very oily or greasy dirt as well as do commercial laundry detergents. “That’s because it doesn’t have many hydrophobic groups,” explains Nagarajan. “But we have found a way to add them and are getting better results.”
The group also plans to confirm that their pectin-based surfactants will eventually break down into harmless substances. And biologists at their university are testing whether it causes allergic reactions in people with sensitive skin. They don’t think it will, but they want to be sure.
For now, Nagarajan and his fellow green chemists have filed an application to patent the pectin surfactant. Meanwhile, several companies have shown an interest in it. So has the EPA: The government agency has provided a grant to fund more of their work on this new family of green chemicals.
Time for a breakdown
Sometimes a chemical’s job is to do harm. Hand sanitizers and soaps that contain antimicrobials — germ-killing chemicals — are two common examples. But their impacts can persist long after use. For instance, after washing down the drain, these chemicals may affect germs in lakes or streams. Some green chemists are now looking for ways to cut the risks posed when such chemicals get into the environment.
Take triclosan (TRY-kloh-san). Its ability to kill germs on hands, kitchen counters and sponges has made it a popular ingredient in a host of products. But data have begun to emerge showing that in the open environment, triclosan’s germ-killing impacts may backfire. How? This chemical might help bacteria resist the killing effects of antibiotic drugs.
Triclosan also can act as an endocrine disruptor. That means it can sometimes mimic the action of hormones. Hormones are potent chemicals. The body produces them to control important activities, such as growth, sleep and reproduction. When the body encounters chemicals that masquerade as hormones, it may inappropriately turn on or off important cellular activities. That can alter how the body develops or can foster disease.
Green chemists would like to eliminate endocrine disruptors. But that’s unlikely to happen. Too many chemicals have this property. And a large number of them have important industrial uses. So the next-best solution would be to find ways to break them down in the environment.
Collins, at Carnegie Mellon University, has worked for more than 30 years studying compounds that do just that. He calls these chemical TAMLs. That’s short for tetra-amido macrocyclic ligands (TEH-tra A-MEE-doh MAK-roh-SIK-lik LIH-gands). As catalysts, these chemicals turn on or speed up chemical reactions. Combined with a reactive chemical called hydrogen peroxide, TAMLs can break down other chemicals very quickly. It takes only a tiny amount to spur many reactions, all without generating harmful pollution.
TAMLs break down triclosan and many other pollutants that pose risks to aquatic plants and animals, Collins’ team has found.
“Endocrine disruptors are changing the makeup of living things. It’s a really big problem,” Collins says. For instance, by acting like hormones (or interfering with hormones), some of these pollutants can alter the development of animals. In some instances, male fish have been feminized. That means the endocrine disruptors led males to look or behave like females. “But we have an unbelievably effective technique for getting rid of [endocrine disruptors].” He says. He’s referring to those TAMLs.
One important concern: TAMLs themselves might be endocrine disruptors. To find out, Collins worked with other green chemists in the United States and Canada to probe that. First, they reviewed lists of known hormone mimics. Then they used computers to predict whether TAMLs might behave in a similar way. For the TAMLs that did, the researchers tested whether those chemicals would bind to cells in the same way that true hormones attach. Next, they analyzed whether these TAMLs also altered the way those cells worked.
Lastly, they tested the effects of TAMLs on fish. For these animal tests, Collins teamed up with Robert Tanguay. He’s a biochemist at Oregon State University in Corvallis. Tanguay works with zebrafish. The small tropical fish are good lab animals. They grow quickly. Their embryos also can develop outside of a mother fish.
The scientists exposed zebrafish embryos to the TAML catalysts being developed for use in water treatment. And even high levels of TAMLs did not alter the growth of the fish.
“We’ve also tested fish swimming around with a TAML catalyst and peroxide, plus a micro-pollutant that feminizes male fish,” says Collins. And still, he reports, “the fish appear to be unharmed.” The last step in their testing process is to see whether TAMLs might have impacts in mammals.
If they prove nontoxic there, too, Collins expects his team’s TAML catalysts will soon find broad use in breaking down toxic water pollutants.
Bright whites, less waste
If you are reading this article indoors, a chemical called titanium dioxide probably surrounds you. This simple white compound reflects light well. So paint makers use it to whiten or brighten their products. It also shows up in other products, including pudding. (In foods, titanium dioxide appears as “E171” in a list of ingredients.) But getting enough titanium dioxide for all of those products isn’t very green.
Titanium is one of the most abundant elements on Earth. It’s a building block of many minerals. Companies mine those minerals, then blend the crushed ore with other chemicals. Finally, they heat the mix to more than 900º Celsius (1,652º Fahrenheit). This takes a lot of energy and creates waste.
In 2013, the EPA gave a Presidential Green Chemistry Challenge Award to the Dow Chemical Co. The purpose? To help the company cut the amount of titanium dioxide a paint needs.
The company’s solution is a new chemical it calls Evoque (Ee-VOKE). Blending it into paint can cut by up to 20 percent how much titanium dioxide is needed.
“One green chemistry goal is to get every bit of value from materials,” explains Mindy Keefe. She’s a senior research scientist at Dow in Collegeville, Pa. That’s why Evoque shows promise, she says. “Using less titanium dioxide saves energy and reduces waste.”
Evoque is a polymer. Polymers are materials made from long chains of a repeating groups of atoms. In paint, the polymer fixes a common problem with titanium dioxide. “Titanium dioxide particles in paint tend to clump together,” explains Keefe. “Evoque forms a shell around them and pushes them apart.” This makes the paint more reflective. It also helps the paint cover surfaces more evenly and completely.
Scientists at Dow worked for more than 10 years to develop the polymer. In green chemistry, such a long investment in time can be well worthwhile. After all, a new product can benefit the environment for much, much longer than that.
“The more serious the hazard is, the more important it is to find green solutions,” concludes Collins at Carnegie Mellon.
antibiotic A germ-killing substance prescribed as a medicine (or sometimes as a feed additive to promote the growth of livestock). It does not work against viruses.
antimicrobial A substance used to kill or inhibit the growth of microbes. Manufacturers have added some, such as triclosan and triclocarban, to sponges, soaps and other household products.
bisphenol A A building block of polycarbonate plastics and many commercially important resins. This chemical gained widespread public attention when research showed it could mimic the activity of estrogen, a female sex hormone.
catalyst A substance that triggers or speeds up a chemical reaction without itself being affected.
chemistry The field of science that deals with the composition, structure and properties of substances and how they interact with one another. Chemists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances.
crude oil Petroleum in the form that it comes out of the ground.
embryo The early stages of a developing vertebrate, or animal with a backbone, consisting only one or a or a few cells. As an adjective, the term would be embryonic.
endocrine disruptor A substance that mimics the action (sometimes well, sometimes poorly) of one of the body’s natural hormones. By doing this, the fake hormone can inappropriately turn on, speed up or shut down important cellular processes.
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.
feminize (in biology) For a male animal to take on physical, behavioral or physiological traits typical of females. It usually results from exposure to an abnormal amount of female sex hormones — or pollutants that mimic these hormones. Feminizing It is sometimes used as a synonym for demasculinizing. In fact, they can be different. A demasculinized male may appear more feminine too, but largely because it had too little exposure to male hormones, not an excess of female hormones.
green chemistry A rapidly growing field of chemistry that seeks to develop products and processes that will pose little or no harm to living things or the environment.
hormone A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body.
hydrogen peroxide A molecule made of two hydrogen and two oxygen atoms. Highly reactive, it can kill many tiny organisms, including germs. Its scientific symbol is H2O2.
hydrophilic Strongly attracted to (or readily dissolving in) water.
hydrophobic Repelling (or not absorbing) water.
mineral The crystal-forming substances, such as quartz, apatite, or various carbonates, that make up rock. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in certain regular three-dimensional patterns).
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).
nonylphenol The name for a family of pollutants that can survive in the aquatic environment persistent for a long time. These chemicals are used primarily to make NPE surfactants and to strengthen certain plastics. Studies have shown these chemicals can mimic the action of estrogen, a female sex hormone. Animals can accumulate these pollutants from the environment. Nonylphenols can be extremely toxic to aquatic organisms.
nonylphenol exothylates (NPEs) A family of chemicals that are widely used in industry as surfactants and wetting agents. When they break down, NPEs produce nonylphenols, a family of chemical compounds that can be toxic to plants and aquatic animals.
patent A legal document that gives inventors control over how their inventions — including devices, machines, materials, processes and substances — are made, used and sold for a set period of time. Currently, this is 20 years from the date you first file for the patent. The U.S. government only grants patents to inventions shown to be unique.
pectin A water-soluble substance that binds adjacent cell walls in plant tissue. Pectins also serve as a thickener in making jams and jellies.
peroxide A group of chemicals that contain a “bivalent” pair of oxygen atoms. Each oxygen atom has an unpaired electron orbiting it that is available to form bonds (attachments) with other atoms. Peroxides are oxidizing agents, meaning that they can react vigorously at room temperatures. Some are used as bleaches.
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
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 Substances whose molecules are made of 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).
polysaccharide A type of carbohydrate made from long chains of simple sugars. Examples of polysaccharides include plant starches and cellulose (a structural material in trees).
sewage Wastes — primarily urine and feces — that are mixed with water and flushed away from homes through a system of pipes for disposal in the environment (sometimes after being treated in a big water-treatment plant).
surfactant A chemical compound that decreases the attraction between water molecules and makes it easier for water to spread on surfaces and to mix with other substances (such as oil).
TAMLs (tetra-amido macrocyclic ligands). A family of compounds developed by chemists at Carnegie Mellon University. By working as catalysts, these chemicals turn on or speed up chemical reactions. Combined with hydrogen peroxide, TAMLs can rapidly break down other chemicals.
titanium dioxide A white, unreactive, solid material that occurs naturally as a mineral and is used extensively as a white pigment.
toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
triclocarban A germ-killing chemical added to some common products such as hand soaps and sponges.
triclosan A germ-killing chemical added to some common products such as hand soaps and sponges.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.
wastewater Any water that has been used for some purpose (such as cleaning) and no longer is clean or safe enough for use without some type of treatment. Examples include the water that goes down the kitchen sink or bathtub or water that has been used in manufacturing some product, such as a dyed fabric.
zebrafish A small tropical freshwater fish belonging to the minnow family. Zebrafish are used frequently in scientific research because they grow quickly and their genetic makeup is well understood.
Word Find (click here to enlarge for printing)
S. Oosthoek. “Plant-powered plastics.” Science News for Students. July 13, 2011.
S. Ornes. “A greener way to keep away flames.” Science News for Students. Sept. 21, 2011.
S. Ornes. “The oily Gulf.” Science News for Students. June 2, 2010.
E. Sohn. “Our plastic world.” Science News for Students. Sept. 26, 2008.
E. Sohn. “Pollution detective,” Science News for Students. June 19, 2006.
A. Stevens. “Cool Jobs: Planet protectors.” Science News for Students. June 21, 2012.
Learn more about the “Twelve Principles of Green Chemistry” from the U.S. Environmental Protection Agency.
Learn more about nonylphenols and nonylphenol ethoxylatesfrom the U.S. Environmental Protection Agency
The Institute for Green Science at Carnegie Mellon University has developed an online course called “Introduction to Green Chemistry.” The course is geared toward students in university and graduate school. However, it contains information useful for younger students as well.
Teachers' questions: Green and clean