In the late 1970's NASA decided to test the feasibility of creating a closed ecological life-support system. In other words they wanted to know if they could create manned moonbases. The first thing they learned was that Skylab had over 300 volatile organic chemicals (VOCs) in the air inside the spacecraft. Not terribly conducive to long term living. A 1980 study disclosed that plants could remove these toxic chemicals.
Aware of the potential for this line of research, the Associated Landscape Contractors of America (ALCA) helped fund a two-year study which tested 12 common houseplants and their ability to remove a variety of toxins from the air. These toxins included formaldehyde, toluene, Chloroform, Ammonia and several other chemicals which are released by common household and building products.
The positive results of this testing, published in 1989, resulted in the formation of the Plants for Clean Air Council (PCAC), a non-profit organization, which supports the cultivation of plant use for indoor air quality control.
To silence the critics who claimed that "sealed-chamber" studies were not applicable to the "real world" NASA created a well sealed structure called "biohome." It contained many toxin producing household items. Tests showed that prior to the introduction of plants, people who entered the biohome would get sick building syndrome - burning eyes and throat, breathing problems, etc. - and the toxin level measured quite high. With the introduction of plant life, people were able to enter with no reactions and the toxin levels were significantly reduced. Pretty darn impressive, no?