It’s common to worry about the air pollution in cities: traffic, industry and some heating systems team up to create an unhealthy environment. Although we tend to think about our homes as a pollution-free space, this is not completely true. Nitrogen oxide and carbon monoxide levels may be lower indoors, but other toxic compounds known as VOCs (Volatile Organic Compounds) are higher indoors than outdoors. Paint, furniture, printers, nail polish removers and other household products are common sources of VOCs.
Short-term exposure to volatile organic compounds can cause eye and respiratory tract irritation, headaches, dizziness, visual disorders, fatigue, loss of coordination, allergic skin reactions, nausea, and memory impairment. Long-term exposure to these compounds is more hazardous. But don’t panic! All these health problems vary with the type of VOC and the more dangerous ones are highly regulated. Yet, some of those less worrying symptoms can team up to produce what’s known as sick building syndrome, which has a great impact on the comfort of the residents and workers.
The NASA experiment
The most common and effective way of getting rid of VOCs is ventilation: windows or ventilation systems. However, houseplants could be a great way to complement ventilation for the improvement of indoor air. One of the first studies on the subject was carried out by the NASA in the late 80s. They worried about air quality in tightly sealed environments, stating that “if man is to move into closed environments, on Earth or in space, he must take along nature’s life support system”. In that study, leaves, roots, soil and associated microorganisms of plants were considered as possible means of lowering the levels of indoor air pollutants. The study concluded that the root-soil area of the plant was the most effective as a VOCs remover. They also designed a combined air filter using a plant and activated carbon.
More recent studies
NASA’s discoveries were later verified by other studies such as this one. They hung 6 potted plants from the ceiling of a classroom and the total VOC average concentrations without and with the presence of potted plants were, respectively, 933 and 249 μg/m3.
Other studies deepen into the different purification systems, including biofilter-adsorption systems such as the one proposed by the NASA. Although houseplants by themselves are a cheap way of reducing toxic compounds, they are not as effective as other purification systems. That’s why combined air filters may be a cost effective solution in the future.
Currently however, the typical indoor air cleaning systems are far more effective for the removal of particles than they are for gaseous compounds such as VOCs. This review suggests that combining them with more or less complex botanical biofiltration systems could also be a suitable solution. The simplest and less effective of these bioreactors is the potted plant.
Potted plants have recently been studied in more depth in sealed chambers. This study was conducted using five common houseplants and some VOCs separately. The plants were jade plant (Crassula ovate), spider plant (Chlorophytum comosum), bromeliad (fam. Bromeliaceae), Caribbean tree cactus (Consolea falcata) and dracaena (Dracaena sspp.). The dracaena absorbed up to 94% acetone (a chemical present in nail polish remover), but the most effective was the bromeliad, removing more than 80% for 5 out of the 6 VOCs studied. Ah, they also made a very cute video:
So, what do we know so far?
- Ventilation and avoidance of VOCs when possible are the more effective ways of keeping your house air clean.
- In potted plants, the foliage must be trimmed so it doesn’t cover up the whole soil, as the root-soil area is the most effective part.
- Potted plants do absorb VOCs, but you’ll have to grow several of them in a room to make it really effective. Remember that 6 potted plants in a classroom made a considerable difference.
- One of the most recent studies suggest that the bromeliad is especially good as a wide range biofilter.
How many indoor plants do you have at home?