The atmosphere of buildings – especially new ones – where we live and work might be full of several chemical compounds that are harmful to our health. In some places, there can be up to 60 different toxic gaseous substances. Fortunately, plants can help purify the air of ill-ventilated buildings.
Volatile Organic Compounds
Several gaseous chemical substances circulate freely in our homes and offices. Some of them, including the infamous volatile organic compounds (VOC), are especially harmful to humans. For example, formaldehyde is a VOC commonly found in interior environments. It is mainly given off by medium density fiberboards (MDF), plywood panels, and wood particle boards, as well as by the adhesives used to fix counters and carpeting. In addition to causing eye, nose and respiratory tract irritation, this gas causes headaches, dizziness, and nausea. Furthermore, formaldehyde is now recognized as being carcinogenic by the International Agency for Research on Cancer (IARC).
Other VOCs, such as acetone, benzene, and toluene, are also present inside some homes and offices. Those pollutants can be given off by various construction materials such as adhesives, insulating foams, paints, varnishes, and carpeting, sometimes for several months or years. They are also given off by some cleaning sprays and various products required to operate photocopiers. In addition to severely irritating mucous membranes, these substances induce unpleasant effects such as drowsiness, headaches, dizziness, and nausea. All of those products can also cause more severe health problems through sustained exposure.
In the early 1970s, NASA asked Dr. B C. Wolverton to find a way to eliminate the volatile organic compounds present in the air of the Skylab 3 space station. The inner atmosphere of the space station was contaminated with over a hundred volatile organic compounds given off by the materials it was made with. To everyone’s surprise, the studies conducted by Dr. Wolverton showed that most houseplants could clean the air of the chemical substances it contains.
During his tests, Dr. Wolverton placed various plants usually grown indoors in a hermetic climatic chamber. Then, he injected polluting substances similar to those found in the Skylab 3 space station – several of which are often found in our homes and office buildings – at comparable concentration levels. After 24 hours, under constant lighting, several plants, such as the golden pothos, English ivy, and peace lily, had accomplished remarkable work by reducing the VOC concentrations by up to 90%!
Towards the end of the 1980s, other experiments on the capacities of air-purifying plants were conducted by NASA scientists in an airtight building called “Biohome”, made with materials giving off high VOC concentrations. The air inside was so polluted that it caused respiratory problems as well as eye and respiratory tract irritation in all who would come into contact with it. Potted house plants were installed around the house to verify their capacity to eliminate the pollutants contained in the air. The results were astonishing. After a few days, the VOCs had almost completely disappeared. One student even lived in the house for a few weeks without feeling any effects.
A living wall is an efficient ‘green machine’ that can clean the air inside buildings. IMAGE CREDIT: Wallemi Living Walls
In his most recent book entitled “Plants, why you can’t live without them”, Dr. Wolverton states that the microorganisms surrounding plant roots also can eliminate air pollutants. In fact, according to him, the microorganisms associated with roots (this association is called “rhizosphere”) can eliminate up to 65% of the VOCs. The plant leaves absorb and metabolize the remaining quantity of air pollutants. Research recently conducted in Canada, Australia, and France confirm Dr. Wolverton’s claims. According to those studies, it seems that the microorganisms contained in soil and water also act as air cleaning agents, sometimes more efficiently than plant leaves.
As a high percentage of the air purifying work is done in the rhizosphere by the microorganisms associated with plant roots, Dr. Wolverton does not recommend growing house plants in soil. Instead, he suggests placing them in containers filled with expanded clay pebbles which allow for proper oxygenation of the roots and microorganisms. Also, the pebbles at the bottom of the containers soak in water, ensuring a constant supply of liquid and nutrients to plants. This growing method allows air cleaning efficiency to increase from 30% to 50%. However, the use of light, high-porosity soil that is rich in compost and sphagnum peat moss is a better environment to host a high number of microorganisms that associate with plant roots.
The plants and the microorganisms associated with their roots have low air-purifying capacities in well-ventilated homes and buildings. This means plants have a maximum efficiency in cities where the atmosphere is highly polluted and in hermetic office buildings where a high proportion of the ventilated air is recycled – sometimes more than 90% – for energy-saving purposes.
In most of the homes located in cities with less pollution, the use of non-polluting materials for construction or renovation works as well as a sound ventilation system (ideally including an air exchange system) to maintain acceptable air quality levels.
Five Effective Air-Cleaning Plants
Areca palm tree (Chrysalidocarpus lutescens)
Rubber fig (Ficus elastica)
English ivy (Hedera helix)
Peace lily (Spathiphyllum wallisii)
Golden pothos (Epipremnum aureum)