Praise Potted Plants

This article updated August 2009
Appeared in Orange Coast Voice newspaper May 2008, page 11.

Potted Plants Ease Indoor Air Pollution
by Sarah S. Mosko, Ph.D.

Australian researchers heeded by Margaret Burchett at the University of Technology have revealed fascinating twists on the potted plant story. Photo courtesy Orange County Voice.

It is a widespread misconception that staying indoors avoids exposure to air pollutants.

Indoor air quality, in fact, is generally worse because contaminants that arise 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, strategies to improve indoor air quality are of interest to nearly everyone.

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 are 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 is also long – the U.S. EPA indicated that more than 900 had been identified in indoor air in a 1989 Report of 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 certain 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 February when formaldehyde fumes sparked the recall of more than 35,000 trailer homes that had been provided to victims of hurricane Katrina by FEMA.

Perhaps even more disquieting than the stealth-like nature of VOCs, many of which are odorless, is their potential to react chemically with one other to produce other potentially unsafe compounds.  A 2006 report commissioned by the California Air Resource 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 U.S. 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 is enough to make breathing indoors seem a bit of a crapshoot.

Reduce Indoor VOCs Naturally
The standard 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.

Nature, however, seems to have provided a very effective alternative that is affordable and requires no electricity . . . the potted plant. The first clues that potted plants are expert at removing air pollutants came from experiments at NASA in the 1980s aimed at finding a solution to the buildup inside tightly sealed spacecrafts of VOCs from synthetic materials. B.C. Wolverton and colleagues demonstrated air filtering capabilities in more than 50 plant species.

Australian researchers headed by Margaret Burchett at the University of Technology have since revealed fascinating twists on the potted plant story. First, the plants per se do not get all the credit since the potting mix microbes living synergistically with the roots do the actual work of removing the pollutants. Soil microorganisms are able to biodegrade 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, 3-6 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.

That plants really do create a healthier indoor environment is supported by other studies reporting significantly fewer worker complaints, such as coughing and fatigue, in offices adorned with plants. Indoor air polluted by VOCs is but an example of the myriad of environmental ills created by the technology that has come to define westernized living. As such, the knee jerk reaction is to reach for a technological solution, e.g. electric air filters. The potted plant stands in sharp contrast and as a humbling testament to the complexity and infinite wisdom of nature. Quoting from one of Burchett’s publications, “the potted plant microcosm represents an adaptive, self-regulating, portable, flexible, low-cost, sustainable and beautiful biofiltration” system for improving indoor air quality.

The VOCs – potted plant saga embodies two important messages: The wanton creation of synthetic consumer products is not without health risks; and man’s survival on earth surely depends on his willingness to live within the embrace of Mother Nature.