Sunday, 10 August 2014

Chemistry: Green and clean

Chemists are finding ways to save energy, cut waste and boost safety.

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.

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.

A surfactant is a chemical that helps liquids mix that would not regularly do so. To accomplish that, one end of the surfactant is hydrophilic (attracted to water). The other end is hydrophobic (repels water).

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.

Fruity alternative

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.

A NASA satellite spotted oil from the 2010 Deepwater Horizon spill off the coast of Louisiana more than a month after the disaster began. Bacteria broke down some of the oil. That inspired a plastics engineer to work on a surfactant that would do the same thing.

NASAThe 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 10 to 15 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.

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 two grants to fund more of their work on this new family of green chemicals.

Scientists used florescent dye and the chemical compound bromide to track the flow of contaminants in river water. Some of these contaminants can masquerade as hormones and affect animals in the environment.
JEFFREY H. WRITER, USGSTime 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.