By Alana Hippensteele
March 4, 2019
There is no doubt that plants are a necessary element of humanity’s ability to comfortably live on this planet. We know that through photosynthesis, plants convert carbon dioxide into oxygen, and through phytoremediation, plants can remove toxins and mitigate pollution in the air.
Yet, questions remain around plants’ effectiveness when cleaning the air in indoor environments. It is now understood that indoor environments can have air pollution that can be several times higher than outdoor environments, making indoor air quality a crucial issue for building occupants’ health. This is especially true since, in urban environments, people spend 80% to 90% of their time indoors.
A famous NASA experiment that was published in 1989 attempted to answer some of the questions around the correlation between indoor plants and air quality, although rather unintentionally. NASA researchers had been looking into ways of effectively detoxifying the air within an enclosed space station environment, when they found that indoor plants had the ability to purify the air of cancer-causing volatile organic compounds like formaldehyde and benzene.
With this information, other scientists began to study the topic further. Scientists at the University of Technology in Sydney, Australia published a study in 2004 that concluded that it was not in fact the plants themselves that most effectively removes toxins, but instead the micro-organisms in the potting mix rhizosphere, or the region of soil closest to the plants’ roots.
Based on the results from the studies, some scientists concluded that house plants are an effective tool for managing indoor air quality. Bill Wolverton, one of the scientists of the original 1989 NASA study, not only advocates for the use of plants as such a tool, but also started a consulting company that supports the use of plants to clean contaminated air, as well as published books on the topic.
Yet there remain scientists who have not yet been convinced of these conclusions. One such scientist, Luz Claudio, a professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai, explained in an interview with Time magazine that, “There are no definitive studies to show that having indoor plants can significantly increase the air quality […] to improve health in a measurable way.” She explained further that the research conducted on the topic only supports the conclusion of plants being capable of removing toxins from the air in an enclosed, sealed laboratory. In the average office building, the conditions are quite different for many reasons, with a key difference being the presence of an air ventilation system.
Hal Levin, a member of the Building Ecology Research Group, discusses this topic of air ventilation further on his blog Building Ecology. Levin explains that the rate of removal of volatile organic compounds by plants “is smaller than the removal of pollutants through the air exchange that takes place in a very tight building due to leakage through the envelope. If you fill a house with three layers of the plants recommended by the advocates, the removal rate would be equal to 1/10th of an air change per hour.”
Hal Levin goes on to explain that extensive use of plants indoors can actually have detrimental effects on indoor air quality, due to “substantial risks of moisture, mold, and bacteria problems in the air.” He also cites issues in relation to the use of fertilizers and pesticides in the indoor environment, explaining that it is beneficial to not keep any plants that require frequent irrigation, fertilizer, or pest control inside or in close proximity to a building for the purposes of maintaining occupant health.
An article published by the International Association of Certified Home Inspection goes on to add that overwatering plants in a workplace environment can “lead to cosmetic and even moisture-related structural problems, as well as mold and other serious indoor air quality issues.” With this in mind, strict regulations in the workplace around the care of plants in the indoor environment are crucial. Furthermore, when considering the selection of plants, it is important to remember that some people also have allergies to certain plants, and most often to flowering plants.
Yet, there are proven benefits of having plants in a workplace environment. Those benefits may not come from improved indoor air quality, but rather from the psychological benefits of being around plants for building occupants. Studies have shown that plants can diminish stress by calming the sympathetic nervous system, and can also contribute to a sense of happiness within an indoor environment. Research clearly supports the idea that spending time around plants significantly contributes to people’s mood and energy levels in a positive way, so although the indoor air may not be purified because of them, plants’ relevance in the workplace environment remains substantial.
Alana Hippensteele is the Editor of American Cleaning & Hygiene.