by Wendy Diaz

Now that we are spending a lot more time indoors due to the cold weather, I decided to investigate the relationship between our houseplants and indoor air quality (IAQ).  IAQ is defined as the level of indoor air pollutants in a building, including carbon dioxide (CO2), moisture, volatile organic compounds (VOCs), combustion products, and particulates¹.  We have houseplants for many reasons:  aesthetic beauty, to continue our garden hobby indoors during the winter season and to protect our tender plants (e.g. bougainvillea); but studies have shown there may be other potential benefits to houseplants other than the well known uptake of carbon dioxide and production of oxygen and natural beauty.

Ever since the publication of the 1989 NASA study², entitled Interior Landscape Plants for Indoor air Pollution and Abatement, there has been much interest and publicity in the media³ about certain plants removing toxic airborne contaminants from our indoor air.  Three chemicals (benzene, trichloroethylene (TCE) and formaldehyde) with known adverse human health effects were injected into Plexiglas chambers containing plants along with activated carbon filters in the original NASA study.  Some of the study results demonstrated removal of low concentrations of benzene and trichloroethylene from the air inside sealed chambers (with activated carbon filter systems) using golden pothos (Scindapsus aureus) and trace amounts of formaldehyde were removed by the green spider plant (Chlorophytum elatum) and also by aloe vera.  The Peace lily (Spathiphyllum “Mauna Loa”) and English ivy (Hedera helix) were also effective in removing benzene from the sealed chambers.  Benzene is a volatile organic carbon (VOC) emitted as a gas from fuel, paints, varnishes, solvents and inks.  Trichloroethylene is used as a commercial metal degreaser and dry cleaning fluids, adhesives, paints and varnishes.  Formaldehyde-based resins are components of finishes, plywood, paneling, fiberboard, and particleboard, all widely used in mobile and conventional home construction as building materials (subflooring, paneling) and as components of furniture and cabinets, permanent press fabric, draperies, and mattress ticking.  

Subsequent research studied the effectiveness of cleaning indoor air of common pollutants such as formaldehyde, nitrogen oxides, sulfur oxides with the spider plant (Chlorophytum comosum), croton (Variegatum) and Peace lily (Spathiphyllum wallisii)⁵.  Another study⁶ demonstrated reduction in ozone by snake plant (Sansevieria trifasciata), spider plant (Chlorophytum comosum) and golden pothos (Epipmnum aureum) using CSTR (Continuously Stir Tank Reactor) chambers.

It is now commonly accepted that houseplants have the potential to clean indoor air and a list of the top 10 ‘houseplant cleaners’ is provided here http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3230460/⁴.  Nevertheless, there has been criticism from the EPA of the NASA study⁷.  The studies were done in sealed experimental chambers and did not directly represent the highly variable environment of an actual building.  Thus, the EPA stated that the ability of plants to actually improve indoor air quality is limited in comparison with common ventilation⁸; and others have stated that further research is needed.⁹  

In fact, houseplants can be detrimental to indoor air quality if they are over-watered and result in the growth of microorganisms that can be harmful to allergic persons¹⁰.  Another factor is that it is far easier to be preventative when maintaining your indoor air quality by using less toxic products in your homes i.e. source control ¹¹, using an air filter and regular cleaning¹².

It may be that houseplants do not significantly clean our indoor air of pollutants or they are not the most effective way of reducing toxic gases in our homes and as such, we should not rely on them for this function.  Alternatively, we should control the sources of the pollution by reducing chemicals and making ventilation improvements in our homes.  Nevertheless, it is well documented that houseplants convert carbon dioxide to oxygen and by looking at green nature we can reduce stress and increase your memory¹³!  Enjoy your houseplants for their beauty and the connection to nature they provide us during these winter months.

In Summary

• Several studies have shown that common houseplants reduced levels of contaminants in the air inside closed, sealed chambers.
• Further research is needed to demonstrate whether houseplants provide the same cleaning effect in the more variable environments found in homes and office buildings.
• Houseplants convert carbon dioxide to oxygen.
• Houseplants can negatively affect air quality if overwatering promotes the growth of microorganisms.
• People can improve air quality in homes and other buildings by using air filtration, cleaning regularly, and choosing less toxic products.

References:

1.  https://energy.ces.ncsu.edu/indoor-air-quality-defined

https://extensiongardener.ces.ncsu.edu/wp-content/uploads/2013/08/2000-022.pdf?fwd=no

2.  http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930073077.pdf
3.  http://www.mnn.com/health/healthy-spaces/photos/15-houseplants-for-improving-indoor-air-quality/a-breath-of-fresh-air https://lenoir.ces.ncsu.edu/2014/12/improve-air-quality-naturally-with-plants-2/
4.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3230460/
5.  http://interesjournals.org/full-articles/correlation-between-some-components-of-interior-plants-and-their-efficiency-to-reduce-formaldehyde-nitrogen-and-sulfur-oxides-from-indoor-air.pdf?view=inline  
6.  http://horttech.ashspublications.org/content/19/2/286.short  
7.  John Girman’s (EPA) analysis of NASA research:  

http://nepis.epa.gov/Exe/ZyNET.exe/000002IB.TXT?ZyActionD=ZyDocument&Client=EPA&Index=1991+Thru+1994&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C91thru94%5CTxt%5C00000002%5C000002IB.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL

8.  http://www.epa.gov/indoor-air-quality-iaq/indoor-air-pollution-introduction-health-professionals#plants-control
9.  http://www.practicalasthma.net/pages/topics/aaplants.htm.
10.  http://www.cpsc.gov/en/Safety-Education/Safety-Guides/Home/The-Inside-Story-A-Guide-to-Indoor-Air-Quality/

11.http://www.epa.gov/indoor-air-quality-iaq/inside-story-guide-indoor-air-quality#source-controls

12.  https://sustainability.ncsu.edu/changeyourstate/improve-home-air-quality/

13.http://www.uvm.edu/pss/ppp/articles/plantswork.html;     http://ellisonchair.tamu.edu/health-and-well-being-benefits-ofplants/#.VqKsMDY6RCM