Tropical Plants Purify, Humidify Air Microbes Break Down Chemicals

Article excerpt

I have an indestructible devil's ivy (Epiprenum aureum) winding its heart-shaped, green-and-gold leaves along a string looped beneath the skylight over my bed. Some call it golden pothos.

Whatever its name, it's one of those dime-store plants that survives when its pot crashes to the floor or you forget to water it for weeks. But I never knew it was a champion air cleaner.

So are the areca palm (Chrysalidocarpus lutescens), the Boston fern (Nephrolepis exalta Bostoniensis), the weeping fig (Ficus benjamina), the peace lily (Spathiphyllum), the corn plant (Dracaena fragrans Massangeana), the lady palm (Rhapis excelsa), the elephant ear philodendron (Philodendron domesticum) and a score of other house plants.

I used to think of these types as rather dull members of the plant world.

But the ability of many tropical foliage plants to clean and humidify the air of bone-dry, stuffy apartments has turned me around. And the latest research, which shows that these plants also suppress bacteria, spores and molds, makes me want them in my house, cleaning my air.

The potential of plants as air purifiers was big news in the 1980s, when Dr. William Wolverton, then a senior scientist at the National Aeronautics and Space Administration, reported the results of his experiments with various plants placed inside sealed chambers that had been pumped full of chemicals such as formaldehyde, benzene, xylene and ammonia.

NASA was trying to identify which plants could clean up the air, after researchers had discovered that the synthetic materials inside Skylab emitted more than 100 chemicals.

"When NASA started looking at how to build a structure on the moon and sustain life, it finally accepted the fact that the only way this can be done indefinitely is to create an Earth environment," Wolverton said. "And what's that? Plants and microbes. Nature."

Over the years, his studies have led to a number of revelations about which plants are good at cleaning up pollutants and how they do it.

Microorganisms in the plant leaves and the root zone appear to break down chemicals. And the type of bacteria that a plant encourages around its roots can mean the difference between a good pollution fighter and a wimp.

Wolverton's most recent report, published in the August/September 1993 issue of The Journal of the Mississippi Academy of Sciences, sums up the cleansing abilities of 30 indoor plants.

The Boston fern is tops at removing formaldehyde from the air; the pot mum (Chrysanthemum morifolium) and the dwarf date palm (Phoenix roebelinii) are close behind.

The dwarf date palm is one of the most effective plants at removing xylene, and the lady palm is a champ at breaking down ammonia. Earlier studies showed that the elephant ear philodendron metabolizes benzene and carbon monoxide, as does my invincible vine, devil's ivy.

Wolverton has concentrated on plants that are easy to grow and rarely plagued by insects. "If I had to choose just one plant, it would be the areca palm," he said.

In 1990, Wolverton left NASA to set up his own research company to promote the use of plants in cleaning the air in energy-efficient, but often poorly ventilated, offices and homes.

"Most people don't know what's in their apartment," Wolverton said. "But formaldehyde, for instance, is in foam insulation, in beds made of veneer, in the backing of rugs and couches, in pressed-wood paneling." Not to mention grocery bags and wax paper, facial tissues and paper towels. Benzene is in tobacco smoke, inks and detergents.

Copying machines, computers and laser printers, as well as solvent-based office supplies, all emit volatile organic chemicals, he said.

If your office or home is energy-efficient, chances are those chemicals are not being replaced by outside air.

"But even if we had no products that pollute," Wolverton said, "people pollute, and the air becomes stagnant. …

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