This houseplant can clean indoor air | Science News for Students

This houseplant can clean indoor air

Adding a rabbit gene helps this ivy break down cancer-causing chemicals
Feb 12, 2019 — 6:45 am EST
a photo of ivy plants inside a wood cabinet there is a fog or mist creeping out from behind the doors

Plants behind the doors of this greenhouse are breaking down harmful chemicals that pollute indoor air.

Mark Stone/University of Washington

Cleaning supplies, paints, glues and other items can release harmful chemicals into indoor air. Removing them from that air can be tricky and expensive. But Stuart Strand thinks houseplants may be able to help.

Strand is an engineer at the University of Washington in Seattle. He studies ways to clean up the environment using plants and other living things.

The idea he’s working with is hardly new. NASA researchers first proposed it in the 1980s. When plants take in air through their leaves, they can use proteins called enzymes to disarm toxic chemicals. But most enzymes only work on a few types of chemicals. And plants may not have enzymes that tackle each of the pollutants in their environment. So plants' usefulness for cleaning up pollution is limited without some help from scientists.

Strand’s team decided to work with a houseplant called pothos (POH-thoes) ivy. They boosted its pollution-breakdown ability by adding a pollution-busting gene. In tests, this altered plant removed some pollution from the air.

Strand hopes such plants will help tackle the widespread problem of home air pollution. Indoor levels of those chemicals tend to be small. But if people breathe them in every day for years and year, they might lead to disease, such as cancer. Small children and teens may get extra-large doses if they spend more time at home than their parents.

Strand’s team starting by giving plants the gene to make an enzyme called 2E1. It’s a liver enzyme shared by all mammals, including people. They used the rabbit version of this gene because they had worked with it before.

This enzyme targets small, carbon-rich molecules called VOCs. (That stands for volatile organic compounds.) VOCs are a big problem. Because they turn into a gas at room temperature, they are fairly easy to inhale. Once in our bodies, VOCs can cause breathing troubles and other problems. They can also damage DNA, increasing the risk of cancer.

Inside the liver, 2E1 can break down VOCs at the molecular level. Strand's team wanted to know whether this liver enzyme would do the same thing inside a leaf. The good news, they found: It does.

One tough plant

The researchers chose to work with pothos ivy — also known as "devil's ivy" — because it's already a popular houseplant. “Even I can’t kill pothos ivy,” Strand says, “and I’m not very good with houseplants.”

They took baby plants that were only a few centimeters tall and put them in bottles. The bottles held just some water, a few nutrients and air.

After sealing the bottles, the researchers injected one of two common indoor VOCs into each bottle. Some bottles received benzene (BEN-zeen). It’s a common ring-shaped carbon-based chemical found in many things, including gasoline. Benzene often enters homes through attached garages. Other bottles got chloroform (KLOR-oh-form). This chemical forms in chlorine-treated water, like tap water. It can escape into the air during hot showers.

a photo of several different pothos plant clippings in sealed bottles in a test tube rack
Scientists tested the air-cleaning power of genetically modified pothos ivy by putting small plants in sealed bottles with polluted air.
Mark Stone/University of Washington

Strand’s team also set up bottles with regular pothos ivy, and bottles with no plant at all. They let all the bottles sit in the lab for more than a week. Each day, the scientists sampled the air inside the bottles. They ran these samples through a machine called a gas chromatograph (Kroh-MAT-uh-graf). It can identify the chemicals in air.

All the chloroform bottles started out with the same amount of the gas. In bottles with the gene-altered ivy, chloroform levels fell 82 percent within three days. Chloroform levels in bottles with regular plants barely budged.

Results with benzene were similar. Its level in bottles with normal pothos dropped slightly over eight days (due to small leaks). It did the same in plant-free bottles. But in bottles with ivy able to make the 2E1 enzyme, benzene plunged by about 75 percent.

Strand and his colleagues shared their findings January 2 in Environmental Science & Technology.

Cleaning house

The results of the experiment confirm that adding 2E1 helped pothos ivy break down common VOCs. But cleaning all the air inside a tiny bottle is easier than detoxifying an entire house.

For one thing, houses and apartments are much bigger. Indeed, a plant in the living room may not be able to clean up air in the kitchen. “If you want to remove [toxic pollutants] from the air and you really want to do it well, you’ve got to move the air past the plants,” Strand says. “You can’t just have the plant sitting over there in a corner.”

VOC levels in homes tend to be much lower than those that Strand’s team tested. The researchers will need to try the ivy in air with very, very small amounts of VOCs, says M. Carmen Martínez. A plant biologist, she works at the Autonomous University of Barcelona in Spain.

In fact, Strand’s team is doing tests to find out whether ivy with the 2E1 gene can clean air in real-world homes. If it works, they hope one day to sell these plants in stores.

Still, there’s one more hurdle such plants will need to clear, says Majbrit Dela Cruz. And that is whether people will be willing to use them.

Dela Cruz is a biologist at the University of Copenhagen in Denmark. She studies how plants interact with chemicals, although not as part of this study. Some people distrust genetically modified organisms, also called GMOs, she notes. They may worry that adding genes to plants will have unexpected effects. Or they may fear that houseplants with rabbit genes will escape into the environment.

Strand will have to prove that 2E1 ivy won’t spread its genes outdoors before getting approval to sell it in the United States. (Pothos ivy can’t survive in cold weather, so in many places it wouldn’t live long enough to cause problems.) Even then, some people may not be willing to bring a plant with rabbit genes into their home. “Whether it’s of use in our homes,” says Dela Cruz, will depend “on whether people will accept that.”

Power Words

(more about Power Words)

autonomous     Acting independently.

benzene     A ring-shaped hydrocarbon molecule made from six carbon and six hydrogen atoms. It’s liquid at room temperature and easily evaporates into the air. It’s widely used in industry and a natural constituent of petroleum, gasoline and cigarette smoke. It is highly toxic if breathed in large amounts and may cause cancer after prolonged, lower dose exposure.

biology     The study of living things. The scientists who study them are known as biologists.

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 exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and 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. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chlorine     A chemical element with the scientific symbol Cl. It is sometimes used to kill germs in water. Compounds that contain chlorine are called chlorides.

chloroform     A colorless, sweet-smelling chemical solvent. Long ago, doctors would have patients inhale vapors of this chemical to render them unconscious — and painfree — during surgery.

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.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

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 (or even the placement of things in the vicinity of an item of interest).

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.

enzymes     Molecules made by living things to speed up chemical reactions.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

genetically modified organisms     Also known as GMOs, such organisms are the result of genetic engineering.

glue     A sticky substance that attaches one material to another.

liver     An organ of the body of animals with backbones that performs a number of important functions. It can store fat and sugar as energy, break down harmful substances for excretion by the body, and secrete bile, a greenish fluid released into the gut, where it helps digest fats and neutralize acids.

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).

NASA     Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

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

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

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.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

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. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

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.

VOCs     See volatile organic compounds.

volatile organic chemicals (VOCs)    Certain solid and liquid chemicals that evaporate (become gases), often at room temperature or lower. Many of these chemicals can be harmful if inhaled or allowed to move through the skin. Concentrations of these chemicals tend to be higher indoors than out. Sources of VOCs include numerous household products, such as paints, varnishes, waxes, oil-dissolving solvents, cleansers, disinfecting, cosmetics, degreasers and glues. Many fuels also release VOCs.

weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.

Citation

Journal: L. Zhang et al. Greatly enhanced removal of volatile organic carcinogens by a genetically modified houseplant, Pothos ivy (Epipremnum aureum) expressing the mammalian cytochrome P450 2e1gene. Environmental Science & Technology. Vol. 53, January 2, 2019, p. 325. doi: 10.1021/acs.est.8b04811.