Purify stale indoor air with plants

In a few years' time, your philodendrons, golden pothos, spider, and similar foliage plants will be able to rid your home of most unwanted odors, including many potentially irritating pollutants. Special electrically powered growing pots will enable them to accomplish this by drawing stale indoor air through the plants' root systems, where it will be purified and released back into the home as pleasant-to-breathe, odor-free air.

Meanwhile, even without the fans to assist them, your potted plants are already doing a lot more to improve air quality in your home than you probably ever realized. Recent discoveries have shown that green leaves do a surprisingly good job of cleaning the air of many impurities on their own.

Growing plants absorb carbon dioxide from the air through their leaves and give off oxygen in exchange. That much has been known for more than a century. But it wasn't until Bill Wolverton, a senior research scientist at the National Space Technology Laboratories in Bay St. Louis, Miss., began working on air quality in the tightly sealed living quarters of space vehicles that anyone believed they might remove many air impurities as well.

Dr. Wolverton says what would work in space would work effectively in the almost capsule-tight, energy-efficient homes that many people are now building. Leaky older homes, while more costly to heat and cool, seldom have indoor pollution problems.

After working with hyacinths on a waste-water treatment system some years back, Wolverton wondered if green leaves might not take pollutants from the air the way roots absorb them from water.

To test his theory, he put two potted spider plants into a sealed enclosure containing vaporized formaldehyde. This gas is given off by many modern building materials and household items - plywood, particle board, carpeting, even paper toweling and tissues, are common examples - and can reach toxic concentrations in tightly constructed homes.

After 24 hours in the test chamber, the spider plants had reduced the formaldehyde by 85 percent. Subsequent tests involving many different plants showed that elephant ear philodendrons are particularly effective. Lacy tree philodendrons and pothos were other useful air purifiers. But Wolverton believes that all green leaves are capable of removing some impurities from the air.

Currently, Wolverton is working on a range of other airborne impurities and preliminary results look promising, he says, in particular the reduction of carbon monoxide and nitric dioxide, both resulting from indoor combustion. (Gas cooking stoves and tobacco smoke are the major contributors.)

Benzene is another common household pollutant that is absorbed and neutralized by growing plants. An exception is cooking gas, whether natural or propane, that escapes before it is burned. It has a decidedly negative affect on many plants. Tomato leaves are particularly sensitive.

At present, some 15 to 20 houseplants are enough to purify the air in the average (1,800 sq. ft.) energy-efficient home, Wolverton believes. He suggests placing ``at least 15 plants downstairs,'' where most of household activity takes place, adding any additional plants you might have in various upstairs rooms.

An attached greenhouse filled with foliage plants would prove most effective, he contends, if fans were used to keep household air circulating continually through the plant room.

A word of caution: Sometimes mildew and fungus can form on the surface of potting soil, which can increase the number of spores in the air. To prevent this fungus, simply cover the surface with a layer of pebbles.

More recent research has shown that soil bacteria, concentrated in and around plant roots, does an even more impressive job than leaves of reducing chemical pollution, by feeding directly on the contaminants.

In the home, the need is to bring the stale air into contact with the plant roots and the bacteria and fungi that live on them. Wolverton's suggestion is to include a high percentage of activated charcoal in the potting soil. A small fan in the pot would draw indoor air through the charcoal, which would trap the pollutants. Bacteria and other microbes on the roots would then feed on the contaminants, rendering them harmless.

These living air purifiers, Wolverton says, should be on the market ``in about five years.''