Do indoor plants really fight indoor air pollution?
Indoor plants brighten our lives by bringing a little touch of nature into our homes and offices.
But beyond their aesthetic and emotional benefits, many people swear that indoor plants also improve our physical health by cleaning the air of toxins.
Is this story about "cleaning out the toxins" just a bunch of hippie hokum, or can houseplants really purify the air?
The Science Behind Indoor Air Quality
In order for a plant to thrive indoors, it has to be tolerant of low-light conditions, stale indoor air, an irregular or indifferent watering regimen, and all the other slings and arrows we humans throw at our plants.
Not all plants, of course, are going to make it indoors, as many a brown-thumb gardener can attest. Even the most cautious of caretakers has thrown out a plant that just seemed determined to die.
And indoor plants certainly have their work cut out for them: The EPA has determined that indoor air can be up to 100 times more polluted than outdoor air.
What pollutants are found in indoor air? You may be sorry you asked. A frightening list of volatile organic compounds, or VOCs -- including benzene, xylene, hexane, heptane, octane, decane, trichloroethylene or TCE, methylene chloride and formaldehyde -- have been found in indoor air.
Additionally, ozone -- the highly reactive, colorless gas that's the main component of smog -- isn't just an outdoor pollutant. Ozone also infiltrates indoor environments since it can be released by ordinary copy machines, laser printers, ultraviolet lights and certain indoor air purifiers.
These pollutants can have serious health impacts. Benzene, for example, is internationally recognized as a cancer-causing agent. Other illnesses, such as asthma and other neurologic, reproductive, developmental, and respiratory disorders are all linked to exposure to VOCs.
And the toxic effects of ozone on humans include pulmonary edema, hemorrhage, inflammation, and a significant reduction in lung functioning. In other words, poor indoor air quality can sicken and kill you.
Phytoremediation to the Rescue
Has anyone ever proven that indoor plants can clean the air of these and other pollutants? After all, a scrawny little spider plant, drooping in a forgotten corner of someone’s office, doesn’t look all that potent of an air purifier.
But indoor plants really don’t have anything to do all day except take in carbon dioxide and other gases from the air, and convert these (plus a little light and water) into the sugar compounds that keep the plant alive.
In 2009, to test the effects of phytoremediation (the ability of plants to clean indoor air), researchers from Pennsylvania State University studied the effects of three common houseplants on indoor ozone levels. The scientists chose snake plant, spider plant and golden pothos to study because of the plants' popularity (primarily due to their low cost, low maintenance and rich foliage) and their reported ability to reduce indoor air pollutants.
To recreate a typical indoor environment, the researchers set up phytoremediation chambers in a greenhouse equipped with a charcoal filtration air supply system in which ozone concentrations could be measured and regulated. Ozone was then pumped into the chambers, and the chambers were checked every 5 to 6 minutes. The study revealed that ozone depletion rates were significantly higher in the chambers that contained plants than in the control chambers without plants.
Indoor Plants and VOCs
Researchers from the University of Georgia in 2009 tested the phytoremediation ability of indoor plants to remove VOCs from the air. A range of popular plants were placed in gas-tight glass jars and were then exposed to benzene, TCE, toluene, octane, and alpha-pinene. The plants were then classified as superior, intermediate, and poor, according to their ability to remove VOCs.
The study concluded that bringing common plants into indoor spaces has the potential to significantly improve the quality of indoor air. Of the 28 indoor plant species tested, Hemigraphis alternata (purple waffle plant), Hedera helix (English ivy), Hoya carnosa (variegated wax plant), and Asparagus densiflorus (asparagus fern) had the highest removal rates for all of the VOCs introduced. Tradescantia pallida (purple heart plant) was rated superior for its ability to remove four of the VOCs.
And in 2011, a team of researchers tested the efficiency of formaldehyde removal in 86 species of plants representing five general classes (ferns, woody foliage plants, herbaceous foliage plants, Korean native plants, and herbs).
The scientists found that Osmunda japonica (Japanese royal fern), Selaginella tamariscina (Spikemoss), Davallia mariesii (Hare's-foot fern), Polypodium formosanum, Psidium guajava (Guava), Lavandula (Sweet Lavender), Pteris dispar, Pteris multifida (Spider fern), and Pelargonium (Geranium) were the most effective species tested. Ferns had the highest formaldehyde removal efficiency of the five classes of plants tested, with Osmunda japonica determined to be most effective of all 86 species, coming in at 50 times more effective than the least efficient species.