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Thursday, June 29, 2006 02:32 pm

Unlikely hero

Use houseplants to reduce indoor pollution

Dear “Earth Talk”: Do houseplants really help to clean indoor air? — Jackson Schlemmer, London, England

One positive result of the 1970s energy crisis was the development and widespread adoption of improved insulation materials to maintain indoor energy efficiency. Unfortunately, many of these materials have compromised indoor air quality because of their tendency to release airborne toxins, including formaldehyde, trichloroethylene, benzene, and other volatile organic compounds.

Much of the synthetic carpeting, upholstery, and paint used indoors also contains sometimes noxious gases that get trapped inside airtight homes and offices and build up gradually over time. Most synthetic air fresheners only make matters worse. With most people spending upwards of 90 percent of their time indoors, it may be no coincidence that cases of asthma and other respiratory diseases have been on the rise in recent years.

The unlikely hero in this scenario may in fact be the humble houseplant. In a landmark 1984 National Aeronautics and Space Administration study, initially commissioned to find ways to clean air in space bases and vehicles, researcher Bill Wolverton found that some common houseplants actually cleaned polluted indoor air. He found that philodendrons and golden pothos excelled at stripping formaldehyde from the air, gerbera daisies and chrysanthemums wiped out excessive amounts of indoor benzene, and pot mums and peace lilies absorbed trichloroethylene, a toxic degreasing solvent.

A later NASA study, also conducted by Wolverton, saw houseplants removing up to 87 percent of toxic indoor air within 24 hours. And a 1994 German study reported that one spider plant could cleanse a small room of formaldehyde in just six hours. Further, English ivy, bamboo palm, and snake plants have been shown to be effective in removing cigarette smoke, as well as noxious odors from carpeting and chemical-laden household cleaners.

Just how can a houseplant be so good at cleansing the air? The reason lies in its basic ability to absorb carbon dioxide from the air while releasing oxygen as part of the photosynthetic process. Houseplants are essentially doing indoors what other plants and trees ordinarily do outdoors.

To maximize the benefits of houseplants in cleaning indoor air, it is generally recommended that one plant be used for every 100 square feet of indoor space. Besides those plants mentioned above, other good indoor-air cleaners include palms, ferns, dracaenas, corn plants, weeping figs, dumb canes, orchids, arrowheads, dwarf bananas and Chinese evergreens.

For its part, the U.S. Environmental Protection Agency recommends opening the windows and letting in some good old-fashioned fresh air as the best antidote to breathing in off-gassed airborne toxins in both homes and offices. But many modern buildings do not permit such exchanges between indoor and outdoor air, and it is in just these situations where houseplants can really make the difference.


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