Many toxic chemicals, including formaldehyde, occur in the air in new buildings. In the preliminary experiment outlined here, plants of Fatsia japonica were grown in pots filled with a mixture of bark, sand and a commercial compost. When one of these filled pots without its plants was put into an airtight, illuminated chamber into which gaseous formaldehyde was introduced, the formaldehyde content of the air slowly fell. But, if a potted plant was put in the chamber, the formaldehyde content of the air fell quickly.
The main investigation involved 82 households in a newly-built apartment complex in South Korea. The members of one group had no plants in their apartments, while another group had a mix of plants in different rooms, including Ficus elastica and Spathiphyllum spp. (living room), Epipremnum aureum (kitchen) and Fatsia japonica (bedroom).
The formaldehyde content of the air was always much lower when plants were present. In addition, the people who lived in apartments containing plants reported fewer symptoms of "sick building syndrome", such as allergic disorders of the eyes, nose and throat.
Improvement of Indoor Air Quality by Houseplants in New-Built Apartment Buildings by Lim, Kim, Yang, Kim, Lee, and Shin (2009). Journal of the Japanese Society for Horticultural Science 78 (4): 456-462. The authors' abstract is available at www.jstage.jst.go.jp/browse/jjshs1 from where the whole article can be downloaded as a PDF.