Cleaning The Air Down Under

Australian environmental researcher finds more proof that indoor plants reduce health risks.

SYDNEY - In an ongoing environmental research project, University of Technology - Sydney Research Associate Ron Wood has discovered even more beneficial facts about how plants clean indoor air. Wood and a team of scientists, including a plant physiologist / ecotoxicologist, biochemist / analytic chemist , microbiologist and environmental / urban horticulturist , conducted experiments based on Dr. Wolverton's NASA Research, but took the experiments a step further.

The project, funded by the Flower Council of Holland and the Australian Horticultural Research Development Corporation, placed three species of plants, Howea forsteriana (Kentia palm), Spathiphyllum var. Petite (Peace Lily0 and Dracaena deremensis var. Janet Craig, in sealed chambers and subjected them to two common indoor toxins, n-hexene and benzene, a known carcinogen.

The experiments repeated Dr. Wolverton's results showing that the plants removed the toxins from the chambers. According to Wood, the removal rate was slow at first, but increased substantially after a few days. He attributes this to biochemical systems that switch onto deal with the toxins - it absorbs and metabolizes them. When the level of toxins was increased, the plants maintained or increased their removal rates.

The project also included an experiment that placed the plants in total darkness - when photosynthesis does not take place and the stomata's are shut, preventing gaseous absorption into the leaves. No reduction in the removal rate occurred. Instead, in some cases, the removal rate increased and improved that light is not necessary for the removal process.

Next the research team added more toxin to the chambers to try achieve saturation or the point where the plants could no longer remove toxins. In the 7 to 10 day timeframe in which the experiments were conducted, the team could not achieve saturation of the plants. This observation led Wood's team to an additional test - on the potting medium. What role do the microorganisms play in the removal process?

For this part of the research, the plants were removed from the chambers and the potting mix was returned with new doses of toxins added. The result: The removal rates remained high, only slightly less than those obtained with the plants present. Even after 7 to 10 days without the plant, the removal rate was maintained.

According to Wood, this means that removal is a biological process and the microorganisms in the potting soil are the rapid-removing agents of the removal system.

To further his findings, Wood decided to test the plant itself. First the roots were washed in sterile water to remove any remaining potting mix and as many microorganisms as possible. The plant was placed in the chamber in a hydroponics solution (no potting mix), under the same conditions as before. Again removal activity took place. In some tests, the removal activity was the same as when the plant was in the potting mix, suggesting that microorganisms must still be present in the root system The difference in the removal rates among the plants suggest that different relationships exists between the plants and their root-associated microorganisms.

The final test was on "virgin" potting mix that has never been associated with a plant. In this test removal was still achieved, but at a much slower rate and at a level lower than with plants, and was exhausted after 9 to 10 days. Wood asserts that these results show microorganisms exists independently in the potting mix, but are unable to grow and reproduce in the absence of a plant, so toxin removal using only potting mix is short-term.

"Our research provides new information about the induction effect, or the "switching on" of a biochemical system to absorb and metabolize a chemical compound," Wood says. " This is new information showing that longer plants are exposed to toxins, the better the plant/soil system works at removing them. This is the first time that this has been demonstrated.'

Wood's team feels these findings reinforce Wolverton's research and provide ample documentation for promoting indoor plants as necessary clean air tools.

According to Wood, who is INTERIORSCAPE magazine's Clean Air Correspondent, the findings are accepted by the International Society for Indoor Air Quality and Climate, the World Health Organization and the United States Environmental Protection Agency (EPA).

In a related study, the EPA recently published its draft of the "Healthy Buildings, Healthy People" report, outlining the problems associated with indoor air toxins (sick-building syndrome) and the need for aggressive programs to address indoor air pollution problems.

In a letter to's 'Scaper Talk, Wood points out, "In the EPA's final draft, among the five goals for upgrading indoor environments is: No. 4 - Create and use innovative products, materials and technologies. I think the EPA's goals present the possibility that living plants indoors enhance people's health and environment. This is more than selling pork against beef. This report should be required reading for all interiorscapers, and the uppermost in the minds of those directing the Growth Initiative."