A NASA scientist, Dr Bill Wolverton, first claimed that houseplants improved indoor air quality in 1989 when results of his experiments were published.  However, since then his claim has been refuted by Professor Michael Waring. 

What’s the truth?  Due to customer enquiries, IAQ’s research asked: Do houseplants purify indoor air and, in so doing, improve air quality?  Firstly, here’s an outline of the experiments undertaken by Dr Wolverton:

Wolverton’s Houseplant Experiments – Methodology

Wolverton, a senior research scientist, was working for NASA at the Stennis Space Centre, when he conducted the experiments.  Plexiglass chambers were constructed and various indoor house plants placed inside them.  Wolverton then introduced chemicals and “scientifically” measured how effective each plant was at absorbing the harmful substances and removing them from the air surrounding them.

Here are some of Wolverton’s findings but please keep in mind, and read on, to see that these were refuted.

Spider Plants and Formaldehyde

Wolverton’s experiments discovered that Spider Plants (Latin Chlorophytum comosum), Philodendrons and Golden Pothos (commonly known as Devil’s Ivy) removed formaldehyde from air.  Formaldehyde is found in everyday household products (such as washing up liquid, fabric softeners and cosmetics and in building and paper products).  In small amounts formaldehyde is known to cause eye, nose and throat irritation.  In large amounts formaldehyde causes skin rashes and lung problems.

Daisies and Benzene

Wolverton also discovered that Gerbera Daisies and Chrysanthemums were “most effective” at removing Benzene from the air.  Benzene, a major component of petrol, is also found in detergents, plastics, solvents and cigarette smoke.  On Benzene the UK government states that:

“Short term exposure to benzene in air may cause irritation to the eyes nose and throat, cough, a hoarse voice and breathing difficulties. Exposure to larger amounts can cause swelling of the airways and a build-up of fluid in the lungs. Ingestion of benzene may cause a burning feeling throughout the digestive tract, nausea, vomiting and pain.

Following exposure by inhalation or ingestion benzene may cause neurological effects, problems with the heart and lungs, coma and convulsions. Benzene may cause redness and swelling if in contact with skin. It may cause a burning and irritation to the eyes…”  CLICK HERE TO READ MORE.

Peace Lilies and Formaldehyde, Benzene, Ethylene Oxide and Ammonia

According to Wolverton, and many writers who have since based their articles uncritically on his experiments, the Peace Lily is at the apex of plants that remove from indoor air.  For instance, I found this reference based on Dr Wolverton’s works:

“This amazing natural air purifier [the Peace Lily] doesn’t just add oxygen to your home; it filters and removes toxins including benzene, formaldehyde, ethylene, and ammonia!”

It would be a reason to stuff your house full of Peace Lilies as, according to Wolverton (but later refuted), they combat not only the detrimental effects of formaldehyde and benzene (as outlined above) but also ethylene and ammonia. Below is an outline of the effects of the latter two which show why these substances too need to be removed from indoor air:

Ethylene Oxide

Ethylene Oxide (according to UK government) “is used as a chemical intermediate in the production of various products including antifreeze, detergents, fibres and bottles”.  “Inhalation of Ethylene Oxide” according to the same UK government article “can cause irritation of the eyes and nose, coughing, burning sensation in the mouth and breathlessness.

In severe cases lung damage can occur. Ethylene oxide can be absorbed into the body via inhalation or skin contact causing headache, stomach upset, fitting, coma and heart problems.” Read more from source here.

Ammonia

Ammonia is used in some cleaning products and fertilisers and in the production plastics, synthetic fibres, dyes, explosives and pharmaceuticals. Exposure to Ammonia, according to The National Institute of Occupational Safety and Health, can be fatal! Read more here.

Houseplants and Air Purification the Unfortunate Truth from Professor Michael Waring

The truth about houseplants and how much we can depend on them for purifying our indoor air quality was outed by the eminent Professor Michael Waring.  In an interview with The Atlantic in 2019, Waring put it bluntly:

“You would have to put 1,000 plants in an office [10’ x 10’ x 8’] to have the same air cleaning capacity of just changing over the air once per hour, which is the typical air-exchange rate in an office ventilation system”.

Click here to read the full article in The Atlantic

Conclusions

Perhaps Dr Bill overstated the effectiveness of a few houseplants in cleaning and purifying the air we breathe in homes and workplaces.  Maybe he allowed the myth which grew out of his 1980s experiments to be perpetuated for some other reason.

Was it a coincidence that, almost twenty years later he published a book entitled Grow Fresh Air: 50 Houseplants that Purify Your Home or Office?  Wolverton’s book, published in 1996, is still available in paperback from Waterstones for £8.99.

True, in controlled environments (such as plexiglass sealed compartments) plants did “take substances out of the air through tiny openings in their leaves” and that “roots and soil bacteria are all important in removing trace levels of toxic vapour” that’s why we need forests and to stop destroying them.

However, the fact is that a small terrace house would need approximately 15,000 plants to clean and purify its air and there would be no room to move.  Also, if plants were the answer to improving Indoor Air Quality, you’d be able to buy them from experts in the Indoor Air Quality sector such as IAQ Services Ltd.  Instead, IAQ Services provides Ventilation Hygiene services.