A Superhero Scrubs the Air: The Mighty Houseplant

The humble houseplant is on the attack. Building on NASA experiments for air purification in

space, scientists are pinpointing plant species—from the peace lily to the asparagus fern—

that are particularly skillful at cleaning indoor air of pollutants that can cause a range of

health problems.


A growing body of global research is showing plants can reduce dust particles and

contaminants, such as formaldehyde and benzene, that come from cigarette smoke, paint,

furniture, building materials and other sources. Big growers such as Costa Farms, based in

Goulds, Fla., and retailers Lowe's and Home Depot now sell plants with tags promoting their

air-cleaning abilities.

"The advantage of plants is you can sometimes solve your problem with $100 of plants or

propagate your own," says Stanley J. Kays, a horticulture professor at the University of

Georgia, which is spearheading plant research with scientists in South Korea. In addition to

studying existing plants, researchers there are trying to see if certain species could be

bred to create super-efficient air cleaners.

Interest in plants as air purifiers—what's called "phytoremediation"—comes amid mounting

concerns about the quality of indoor air. People spend more than 90% of their time inside,

where levels of a dozen common organic pollutants can be two to five times higher than

outside, according to the Environmental Protection Agency. Associated health problems range

from headaches and asthma to respiratory diseases and cancer. The agency says it is

particularly concerned about air quality in homes that have taken steps to be more energy-

efficient by adding insulation and other weatherization techniques.

That said, plants aren't yet recognized as a mainstream air-filtration tool. The EPA says

"there is currently no evidence … that a reasonable number of houseplants can remove

significant quantities of pollutants in homes and offices." The U.S. Green Building Council,

which certifies buildings based on environmental standards, says while "using plants to help

clean air is a great strategy…we've had difficulty quantifying the results."

That could be changing. Studies conducted over the past five years by the University of

Technology, Sydney found that small groups of the Janet Craig and Sweet Chico plants placed

in offices with high airborne concentrations of volatile organic compounds consistently

reduced total VOC levels by up to 75%. Reductions to negligible levels were maintained over

the course of five- to 12-week periods studied. "Potted plants can provide an efficient,

self-regulating, low-cost, sustainable bioremediation system for indoor air pollution,"

researchers concluded.

In another study at Washington State University, dust was reduced as much as 20% when a

number of plants were placed around the perimeter of computer lab and small office for one

week.

Margaret Burchett, a professor who led the Sydney studies, estimates that six or more plants

in a 1,200- to 1,500-square-foot house could achieve noteworthy contaminant reductions. At

work, "if you have a couple of nice plants sitting on your desk, it will help purify the air

you breathe," says Bill Wolverton, author of the new book "Plants: Why You Can't Live Without

Them," and one of the NASA scientists who studied plants.

Indoor-air pollutants come in two primary forms: particle pollution, such as dust, pollen,

animal dander and smoke, and gaseous pollutants such as VOCs that are emitted from sources

such as building materials, dry-cleaned clothing and aerosol sprays.

Plants clean the air, researchers say, primarily by absorbing pollution through small leaf

pores called stomata, and via microorganisms living in the potting soil or medium that

metabolize contaminants. Scientists believe plants can begin removing pollution the moment

they're placed in a room and can be particularly useful in spaces where there's little

outside ventilation.

Pinpointing specific air quality problems can be tricky. Do-it-yourself kits and

environmental companies can conduct air-quality tests at consumers' homes. But interpretation

of the results can be confusing because there's no universal national standard for acceptable

levels of many VOCs, according to the EPA.

As for remedies, ventilation often works best, but not every climate is suitable for open

windows and doors. Mechanical ventilation units that remove stale air from a home and provide

fresh outdoor air can cost $600 to upwards of $2,500, not including installation. Indoor air

-cleaning devices using HEPA and activated carbon or ultraviolet-light technology have some

limitations and may require filter changes.

That's why researchers see opportunity for indoor plants, which are inexpensive and

relatively easy to find and maintain. In 2009, UGA scientists identified five "super

ornamentals"—plants that showed high rates of contaminant removal when exposed in gas-tight

glass jars to common household VOCs, such as benzene (present in cigarette smoke) and toluene

(emitted from paints and varnishes). They are: the purple waffle plant, English ivy,

asparagus fern, purple heart plant, variegated wax plant.