Greenery filters out indoor air pollution.

Greenery filters out indoor air pollution

Perhaps because they're so easy to grow, spider plants have seldom shared the cachet of such other houseplants as the African violet, amaryllis or asparagus fern. But preliminary NASA research a few years ago raised the spider plant's prestige when it showed these hanging plants could filter toxic organic pollutants from indoor air. Indeed, "we thought there was something magic about the spider plant," recalls Bill C. Wolverton at NASA's John C. Stennis Space Center in Bay Saint Louis, Miss. But the two-year study he described at a press conference this week in Washington, D.C., suggests most houseplants can remove indoor air pollutants -- whether at home or in a space station. In fact, Wolverton says, compared with the Gerbera daisy, potted mum and banana (Musa oriana), the spider plant is only second-rate.

The new study, funded by NASA and the Associated Landscape Contractors of America, tested the ability of 14 houseplants to remove three volatile organic chemicals: the carcinogen benzene, trichloroethylene (TCE) and formaldehyde. Researchers chose these three not only because they represent a wide range of chemicals found to taint indoor air but also because of suspicions that they contribute to "sick building syndrome" -- the human respiratory complaints and fatigue sometimes associated with occupation of new and newly renovated buildings (SN: 9/23/89, p. 206).

Each plant spent a day in a sealed chamber containing air tainted with one of the chemicals. Pollutant concentrations in the air ranged from 20 or 30 parts per million (ppm) to less than 1 ppm -- concentrations "one might find in a home," Wolverton says. While all plants scavenged the pollutants to some extent, their efficacy varied widely. English ivy, for example, removed 90 percent of the benzene in one test but just 11 percent of the TCE in another. And Ficus removed 50 percent of the formaldehyde but filtered out only about 10 percent of the TCE. Potted mums proved more consistent. In one set of tests they scavenged 61 percent of the formaldehyde, 53 percent of the benzene and 41 percent of the TCE.

In the case of Dracaena, Sansevieria and other plants requiring low light, NASA data indicate leaves accounted for at most 20 percent of the observed pollutant scavenging. Roots and soil microbes, which apparently feed on the pollutants, accounted for the rest, Wolverton says. This may explain why air cleaning proved most efficient when a plant's soil was unshielded by rocks or low-hanging leaves.

Though preliminary, these data suggest that one 10- to 12-inch potted plant per 100 square feet of floor space could dramatically reduce low-level pollution from organic chemicals, Wolverton says. When it doesn't, he suggests supplementing the greenery with fan-driven plant filters he developed at NASA several years ago. The filters root plants directly into activated carbon, supplemented with a little potting soil. A small fan draws room air through the carbon, which collects and holds organic pollutants until microbes and plant roots can degrade them. Commercial versions should be marketed widely within a year, he says.

While the NASA data are "interesting," says Betsy Agle with EPA's indoor-air division in Washington, D.C., they still leave some important questions unanswered--such as how much pollution a plant can filter out before getting sick itself. But EPA's greatest concern, she says, is that people may be tempted to rely on such systems instead of focusing on removing the sources of unhealthy contaminants.