Garden Detective: Houseplants that clean the air

Like pets, indoor plants have long been known to reduce stress. The findings aren’t anecdotal, either.

A 2016 study by Korean and Japanese researchers reported in the Journal of Physiological Anthropology set out to find whether interaction with indoor plants can alleviate the "great deal of stress to modern people" caused by "information technology." The male young adult subjects were divided into two groups, one tasked with repotting an indoor plant and the other with completing an assignment on a computer. When their tasks were completed, the groups switched roles, and the researchers found "significant" differences in blood pressure and heart rate variability that showed "interaction with indoor plants may reduce psychological and physiological stress by suppressing autonomic nervous system activity."

And the landmark 1989 NASA Clean Air Study revealed that plants are the most efficient (and cost-effective) method of reducing indoor air pollution, removing such toxins as benzene and formaldehyde from the air.

If you think those can’t possibly be in your home, think again. If you’ve got carpeting, vinyl flooring, upholstered furniture, plastic grocery bags, cigarette smoke or even a roll of paper towels laying around, you might be inhaling toxins on a regular basis. Ironically, scented air fresheners can exude harmful chemicals into our breathing space. 

Opening a window and running a fan is the most effective way of replacing contaminated air with fresh air, but because airborne chemicals are mostly colorless, odorless gasses, we can’t rely on our senses to alert us to take action. In addition, our climate isn’t conducive to keeping the windows open 24/7 year-round.

The good news is that for low levels of toxins, such as those likely to be found in the average home, ordinary houseplants can help.

We already know the symbiotic relationship we humans have with plants: They provide us with the oxygen we need, and we exhale the carbon dioxide they require. Their absorption of our discarded carbon-dioxide filters — or cleans — the air for us. But plants can absorb many other gasses, including volatile organic compounds (VOCs) and other indoor air pollutants.

In 2016, Vadoud Niri, a chemist at SUNY Oswego, released findings from his research that proved common houseplants are effective in removing harmful compounds from the air. After a visit to a nail salon with his wife during which he became alarmed at the ambient odor from VOCs from nail polish remover, Niri set out to build upon the landmark NASA study. He found that in just 12 hours, a single bromeliad removed 80% of six different compounds from the air; dracaena was extremely efficient at removing acetone, an ingredient in nail polish remover; and spider plants drastically reduced the amount of VOCs in the air immediately upon exposure.

Flowering plants, such as chrysanthemums and gerbera daisies, are most effective at removing benzene from the air. The chemical is found in many household detergents, inks, dyes, synthetic fibers, tobacco smoke, and plastic and rubber products. Long-term exposure to benzene can result in a decrease in red blood cells and can damage the immune system, plus the U.S. Department of Health and Human Services has associated benzene exposure with an increased risk of cancer.

Conventional golden pothos has been shown to reduce the amount of environmental chloroform, a suspected carcinogen found in small amounts in chlorinated water and released into the air when we shower or boil that water.

Philodendrons, spider plants and golden pothos are most effective at removing formaldehyde from the air. The chemical has been found to exude from carpeting, cleaners, foam insulation, furniture, paper products, plywood and particle board. The U.S. Centers for Disease Control and Prevention has associated formaldehyde with sore throats, coughs, scratchy eyes, nosebleeds and breathing difficulty or asthma in those who are susceptible; and the Environmental Protection Agency considers it is “probably [a] human carcinogen.”

And if you bring dry-cleaned clothing, adhesives, inks, dyes, lacquers, paints, varnishes and paper products into your home, chances are that trichloroethylene is hitching a ride in with them. The CDC has twice proposed bans on the chemical, which it has linked to cancer, skin, respiratory and central nervous system effects, and risks to a developing fetus after just a single exposure. Yet, trichloroethylene is still present in many of these products.

In response to these concerns, researchers at the University of Washington have genetically modified the common pothos plant to convert benzene and chloroform into harmless compounds the plants can use to support their own growth, essentially removing the chemicals from the environment. Their findings were reported in the Dec. 19, 2018, issue of Environmental Science & Technology.

The genetically modified pothos plant, which removed 90 percent of the compounds from the air in one week (versus 10 percent for conventional pothos) isn’t yet available for purchase, but conventional pothos offers a measurable benefit.