A friend of mine is moving and asked me whether I know about plants that purify the air. I had to say no… and that made me instantly research the topic. For him, for me and for you. Because I know many people would want to improve their indoor air if they didn’t have to spend two days on finding proper information on the internet. That’s why I did that for you 😉
Here are my results:
“Because Americans spend nearly 90% of their time indoors and nearly 25% of US residents are affected by poor IAQ (indoor air quality) either at the workplace or at home, the US Environmental Protection Agency (EPA) ranks poor IAQ among its largest national environmental threats”. The same goes for the European Environmental Agency.
“In fact, some buildings contain such high levels of contaminants that they are qualified as “sick” because exposure to them results in multiple sickness symptoms (e.g. headache, fatigue, skin and eye irritations, or respiratory illness) commonly described as the “sick-building syndrome” (SBS)”.
“Indoor air contamination is a complex problem involving particles (such as dust and smoke), biological agents (molds, spores), radon, asbestos, and gaseous contaminants such as CO, CO2, NOx, SOx, aldehydes and VOCs (Volatile Organic Compounds). The latter are strongly suspected to cause many Indoor Air Quality (IAQ) associated health problems and “sick-building” symptoms”.
That sounds pretty scary. So what to do?
“Natural aeration is the easiest alternative but it is often not possible because of outdoor weather, external pollution conditions or issues of security, safety in high buildings, climate control, or noise. Periodical air refreshing is often not efficient because many indoor air pollutants are constantly released”. That doesn’t mean you should not periodically open your windows but it means that there has to be done more to get rid of the indoor toxins permanently.
|Filtration||Air is passed through a fibrous material (often coated with a viscous substance), which is efficient for particle removal but not gases. Filters are compact and commonly used but their efficiency decreases as they become saturated (fouling). Microorganisms can also develop in filters and particles reemission might occur.|
|Electrostatic precipitator with ionization||An electric field is generated to trap charged particles. Electrostatic precipitators are often combined with ion generators that charge particles. Remove particles efficiently, are compact, commonly used but can generate hazardous charged particles.|
|Adsorption||Air pollutants are adsorbed onto activated carbon or zeolites, often as filtration post-treatment. The adsorbent might be too specific and might saturate fast because the pollutant are not destructed. There is therefore a potential risk of pollutant reemission.|
|Ozonation||Ozone is generated to oxidize pollutants. Only remove some fumes and certain gaseous pollutants and might generate unhealthy ozone and degradation products. Ozone-based purifiers are not recommended by the American Lung Association.|
|Photolysis||High energy ultra violet radiation oxidizes air pollutants and kills pathogens. It can however only remove some fumes and some gaseous pollutants and might release toxic photoproducts. Accidental exposure to UV light is harmful and UV irradiation is energy consuming.|
|Photocatalysis||High energy ultra violet radiation is used in combination with a photocatalyst (TiO2) to generate highly reactive hydroxyl radicals that can oxidize most pollutants and kill pathogens. This energy-intensive method is increasingly popular and suitable for a broad range of organic pollutants.|
|Membrane separation||Pollutants are passed through a membrane into another fluid by affinity separation. This method is normally recommended for highly loaded streams and has yet to be proven at low VOC levels. If the separated VOCs are not reused, membrane filtration must be completed with a destruction step.|
|Enzymatic oxidation||Air pollutants are transferred into an aqueous phase where they are degraded by suitable enzymes Little information is however available concerning the efficiency of the commercial system and new enzymes must be supplied periodically.|
|Botanical purification||Air is passed though a planted soil or directly on the plants. The contaminants are then degraded by microorganisms and/or plants, the precise mechanisms being unclear. Although the efficiency of botanical purification has not been fully proven, a number of devices have been patented and several commercial products are available.|
|US patent 6,676,091 for instance discloses a device where air is forced directly through a vertical (or slightly inclined) porous material serving as support for hydroponic plants, the plant’s main purpose being to support the activity of pollutant degrading microorganisms in their rizosphere. This device is rather large in regards to other technologies but can be use for interior design purposes.|
|Biofilters and biotrickling filter||Air is passed through a packed bed of a solid support colonized by attached microorganisms that biodegrade the VOCs. In one configuration, air was purified through lava rocks covered with a geotextile cloth supporting mosses|
Which one do you consider interesting the most?
The botanical purification method is our focus in this article, meaning the use of plants to clean indoor air by removing toxins from the air, water and soil, also called Phytoremediation. This method is cost-effective, efficient (some paper say more, some paper say less) and has an aesthetic benefit, too.
“It has been previously demonstrated that formaldehyde and other VOC removal is due to biological action of plants and microorganisms. Plants have been shown to uptake air pollutants via their stomata during normal gas exchange and various pollutants have been shown to be sequestered or degraded in situ or after transfer to other areas in the plant. In addition to the stomata, the root zone has been shown to be an important contributor to the removal of VOCs. Rhizosphere microorganisms [that are connected with or near the root of the plant], found in the growing media, have been identified as significant direct agents of VOCs removal”.
It has been found out that “plants effectively reduced levels of benzene, ammonia, formaldehyde, nitrogen oxides and particulate matter” (extra article on this coming soon). “Plants have also been shown to increase indoor relative humidity by releasing moisture into the air thus increasing the comfort level in sealed environments. Others have linked the use of plants with improved productivity and wellbeing and observed that indoor plants are beneficial for mental health“. I truly believe that 😉
You don’t think your house could ever be contaminated? Read this.
“An average home of 167 m² heated area with 2.5 m ceilings (1,800 ft² with 8-ft ceilings) has a total volume of 418 m³ and would outgas daily approximately 482,000 µg formaldehyde. In addition, cooking with a gas stove would add an estimated 100,000 µg formaldehyde to bring the total formaldehyde to 582,000 µg.”
Now comes the funny part:
“[…] one spider plant in a 3.8 l (1 gal) pot can effect the removal of 7,000-8,000 µg CH2O/d. To meet the air purification needs of the home just described, approximately 70 spider plants (3.8 l pot size) would be needed to purify the air continuously”.
Funny right? Start gathering what you caaaan. Note that some papers had different numbers and that these are only data for formaldehyde.
source: Foliage Plants for Removing Indoor Air Pollutants from Energy-efficient Homes 1 B. C. Wolverton et al.
But it’s not only formaldehyde we should try to avoid and not only our home where we should counteract air pollution. There was a study specifically on offices that states the predominant VOCs were benzenes (toluene, ethylbenzene and xylene) that were released in vehicle fuel emissons and “cause symptoms including dizziness, loss of concentration, nausea and respiratory difficulties via short-term exposure.” Perfect for the office… But chronic exposure can even result in “neurotoxicities, respiratory disease and possible teratogenic effects, while benzene and xylene are confirmed carcinogens”.
source: the potted-plant microcosm substantially reduces indoor air VOC pollution: I. office field-study by R. Wood et al.
Instead of being afraid (quite reasonable though…) what I conclude from this is:
- you can never have enough plants
- keep the soil moist so that microorganisms can do their work (the plant itself often only has the purpose to manage good living conditions for the microorganisms that do the main job)
- try plant pots that allow air circulation at the soil level so that there are better chances for a contact between toxins and soil microorganisms
I will post an article with all the plants that are beneficial for your home and office and remove toxins very soon. Subscribe to my blog via WordPress or mail if you don’t want to miss this!