Houseplants are not only aesthetically pleasing giving a touch of color to otherwise drab offices or houses, they also combat indoor air pollution, particularly with their ability to remove volatile organic compounds (VOCs) from the air. These compounds are gases or vapors emitted by solids and liquids that may have adverse short- and long-term health effects on humans. But in addition to giving off oxygen and sucking out harmful VOCs, a new study has shown that some indoor plants actually release VOCs into the environment.

A research team at the University of Georgia’s Department of Horticulture conducted a study to identify and measure the amounts of VOCs emitted by four species of popular indoor potted plants and to note the source of VOCs and differences in emission rates between day and night. The four plants they chose were Peace Lily (Spathiphyllum wallisii Regel), Snake Plant (Sansevieria trifasciata Prain), Weeping Fig (Ficus benjamina L.), and Areca Palm (Chrysalidocarpus lutescens Wendl.).

Samples of each plant were placed in glass containers with inlet ports connected to charcoal filters to supply purified air and outlet ports connected to traps where volatile emissions were measured. The results were compared to empty containers to verify the absence of contaminants. A total of 23 volatile compounds were found in Peace Lily, 16 in Areca Palm, 13 in Weeping Fig, and 12 in Snake Plant. Some of the VOCs are ingredients in pesticides applied to several species during the production phase.

And it turns out the plants themselves aren’t the only ones responsible for the release of VOCs. Micro-organisms living in the soil were also to blame for releasing volatiles into the atmosphere along with the plastic pots containing the plants, which were the source of 11 of the VOCs – several of which are known to negatively affect humans.

The study also found that VOC emission rates were higher during the day than at night in all of the species, and all classes of emissions were higher in the day than in the night. This was expected as the rate of release is determined by the presence of light along with many other factors that affect synthesis.

The study concluded that, although ornamental plants are known to remove certain VOCs, they also emit a variety of VOCs, some of which are known to be harmful to humans and animals. However the researchers did go on to say that the longevity of these compounds hasn’t been adequately studied, so their impact on humans is unknown.

That plant sitting in the corner isn’t looking quite so attractive now, is it? But before you relegate any plants to the garbage consider this. If the plastic pots were found to be the source of 11 VOCs, you’ve got to thankful the plants at least remove some VOCs as well as emitting them – the same can’t be said for the mass of plastic that probably surrounds you right now. Maybe give that plant some water instead.

The study, Volatile Organic Compounds Emanating from Indoor Ornamental Plants, appears in the American Society for Horticultural Science journal HortScience.