Plants for Purification

Indoor Air Pollution is a Serious Problem—Nature Provides a Simple Answer

Add a Peace lily to your office to keep the air clean.
© wikipedia

Eliminating indoor air pollution can be as simple as dotting your house or office with potted plants, according to research stretching back as far as the space program of the 1980s.

It's a widely held misconception that staying indoors avoids exposure to air pollutants. Indoor air quality, in fact, is usually worse because contaminants that emanate from a vast assortment of consumer products add to the pollution that drifts in from the outside.

Given that urban dwellers pass 90% of their time inside, any strategy to improve indoor air quality is of widespread interest, especially one as appealing and environmentally sustainable as adding potted plants to the décor.

Indoor Air Chemistry

The chief forms of pollutants generated indoors are known as volatile organic compounds (VOCs) that off-gas primarily from common petroleum-based products. They're impossible to avoid since the sources are nearly endless: furniture, carpeting, paints, varnishes, paint strippers, synthetic building materials, air fresheners, cleaning solutions, toilet bowl deodorizers, personal care products, tobacco smoke, pesticides, and solvents in inks and adhesives.

The number of VOCs in indoor air is also long — the U.S. Environmental Protection Agency (EPA) enumerated more than 900 in a 1989 Report to Congress. While some pose no known danger to health, others are linked to acute and chronic health effects like asthma, impaired lung function, or damage to liver and kidneys. Mixtures of VOCs are generally thought to be the cause of Sick Building Syndrome in which sensitive individuals experience symptoms of headache, nausea, and/or eye, nose and throat irritation in specific indoor settings.

Some VOCs are even known to be carcinogenic, like benzene in tobacco smoke, perchloroethylene (aka "perc") in dry-cleaning fluid, methylene chloride in paint strippers, and formaldehyde in pressed wood products like particleboard. That indoor air concentrations of VOCs can reach unhealthy levels was highlighted in 2008 when formaldehyde fumes sparked the recall of more than 35,000 trailer homes that had been provided to victims of hurricane Katrina by the Federal Emergency Management Agency.

Dr. B.C. Wolverton"s latest book explains the rationale behind using plants for indoor air purification.

Perhaps even more disquieting than the stealth-like nature of VOCs, many of which are odorless, is their potential to react chemically with one another to produce other potentially unsafe compounds. A 2006 report commissioned by the California Air Resources Board, for example, outlined how compounds called terpenes, used in air fresheners and household cleaning agents because of their pleasant odor and solvent capabilities, react with ozone to produce formaldehyde along with various particulate pollutants.

According to the EPA, about a dozen common VOCs are consistently found at two to five times higher levels inside homes than out, even in rural settings. Certain activities, like paint stripping, can elevate VOCs by a factor of 1,000. When you add in unpredictable chemical reactions among VOCs, it's enough to make breathing indoors seem like a crap shoot.

Reduce Indoor VOCs Naturally

The mainstream approach to lowering VOCs has been to install commercial air filtering devices or room ventilation systems that exchange room air for outdoor air. Both run on electricity, so they increase electric bills and ultimately add to overall atmospheric pollution by way of burning fossil fuels to produce that electricity.

In the humble potted plant, nature has provided a very effective alternative that is affordable and requires no electricity.

The first clues that potted plants are expert at removing air pollutants emerged decades ago during experiments at NASA aimed at finding a solution to the buildup inside tightly sealed spacecrafts of VOCs from synthetic materials. NASA scientist Dr. B.C. Wolverton and colleagues demonstrated air filtering capabilities in dozens of plant species.

Australian researchers headed by Dr. Margaret Burchett at the University of Technology have since revealed fascinating twists on the potted plant story. First, the plants don't get all the credit since the potting mix microbes living synergistically with the root system do the actual work of removing the pollutants. Soil microorganisms are able to biodegdrade the VOCs by using them as a food and energy source. The plants" job, in turn, is to nourish the root-zone microbial community.

Second, soil microbes exhibit smarts in that, with repeated exposure to a given VOC, they're able to remove it from air more quickly. The microbes are thus ever adapting to the VOCs they encounter.

Burchett has demonstrated the efficacy of common houseplants, like the peace lily or dracaena "Janet Craig," in real life settings with or without air conditioning. In single occupancy-sized offices, three to six plants kept the total load of all VOCs to below 100 ppb, the equivalent of "very clean air." The plants even proved adept at removing highly toxic carbon monoxide.

Top Ten Picks

In a 1997 book titled "How to Grow Fresh Air: 50 House Plants that Purify Your Home or Office," Dr. B.C. Wolverton rates interior plants for air purification abilities along with ease of maintenance and resistance to insect infestation. He recommends at least two healthy sized plants per 100 square feet to maintain good air quality. Currently, his top 10 picks are:
"Areca palm
"Lady palm
"Bamboo palm
"Rubber plant
"Janet Craig
"English ivy
"Boston fern
"Peace lily
"Corn plant
"Golden pothos

Dr. Wolverton also promotes hydrocultured interior plants which he says increase air purification by 30-50% over plants in soil. His new book on the topic—Plants: Why You Can't Live Without Them—explains how inert pebbles that replace the potting soil give better results and also take the guesswork out of maintaining optimal soil moisture.

Indoor air polluted by VOCs is but an example of the myriad environmental ills created by the technology that has come to define westernized living. The kneejerk reaction is to reach for a technological solution like electric air filtration. But the potted plant stands as an awe-inspiring testament to the complexity and infinite wisdom of nature.

SARAH MOSKO, PH.D., is an environmental writer and sleep expert living in California who blogs at sarahmosko.wordpress.com.